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1. Soybeans are rich in protein. Raw soybeans, however, may contain a trypsin inhibitor. This is a chemical which prevents the digestion of protein. The presence of this trypsin inhibitor is genetically controlled. A single gene has alleles TA, TB and TC each of which codes for a different sort of trypsin inhibitor. These alleles are codominant so plant with the genotype TATB will produce two sorts of trypsin inhibitor, inhibitor A and inhibitor B. A fourth, recessive allele, To does not code for a trypsin inhibitor. This information is summarised in the table. (a) Allele Inhibitor produced TA A TB B TC C To None The inheritance of trypsin inhibitors in soybeans is an example of multiple allele inheritance. Explain how multiple allele inheritance differs from polygenic inheritance. ................................................................................................................................... ................................................................................................................................... (1) (b) (i) Give all the possible genotypes of a plant which only contains inhibitor A. ........................................................................................................................... (1) (ii) Give all the possible genotypes of the gametes produced by a plant which contains inhibitors B and C. ........................................................................................................................... (1) (c) Two soybean plants were crossed and the seeds collected and counted. The results are shown in the table. Inhibitors present in seed Number of seeds A and B 23 A 25 B 48 Sir George Monoux Sixth Form College 1 (i) Complete the genetic diagram to explain the results of this cross. Phenotypes of parents:.................................. ....................................... Genotypes of parents:.................................. ....................................... Genotypes of gametes ...................................................................................... Genotypes of offspring: .................................................................................... Phenotypes of offspring Inhibitor A and Inhibitor B Inhibitor A Inhibitor B (3) (ii) A chi-squared test was applied to the data collected in this investigation. Explain why statistical tests such as the Chi-squared test should be carried out on data like these. ........................................................................................................................... ........................................................................................................................... ........................................................................................................................... (2) Sir George Monoux Sixth Form College 2 An investigation was carried out on the insects living on bean crops. The graph shows the relationship between the biomass of primary consumers, secondary consumers and producers. 100 Primary consumers 90 80 70 60 Consumer –2 biomass/g m 50 40 30 20 Secondary consumers 10 0 0 200 400 600 Producers biomass/g m (d) 800 1000 –2 Briefly describe how the data on the biomass of the producers might have been collected. ................................................................................................................................... ................................................................................................................................... ................................................................................................................................... ................................................................................................................................... (2) Sir George Monoux Sixth Form College 3 (e) (i) In this investigation, the efficiency with which the energy in sunlight was converted into energy in the biomass of the producers was found to be 4%. For every 10 000 kJ of light energy falling on the beans, 400 kJ was therefore converted into energy in producer biomass. Use the data in the graph to complete the diagram below which shows the amount of biomass in the primary consumers and the secondary consumers. Energy in sunlight 10 000 kJ 4% Energy in producer biomass 400 kJ ......... % Energy in primary consumer biomass. ...... kJ ......... % Energy in secondary consumer biomass. ...... kJ (2) (ii) Explain why not all of the energy in producer biomass can be converted into energy in primary consumer biomass. ........................................................................................................................... ........................................................................................................................... ........................................................................................................................... (2) (Total 14 marks) 2. Hares are small mammals similar to rabbits. The diagram shows how some of the hares found in southern Africa are classified. Sir George Monoux Sixth Form College 4 Animalia Chordata Mammalia Lagomorpha Leporidae Lepus Pronolagus Pronolagus randensis Jameson's hare Pronolagus rupestris Smith's hare Sir George Monoux Sixth Form College Pronolagus crassicaudatus Natal rock hare Lepus capensis Cape hare Lepus saxatilis Scrub hare 5 (a) (i) Name the genus to which the scrub hare belongs. ........................................................................................................................... (1) (ii) Name the order to which the Natal rock hare belongs. ........................................................................................................................... (1) (b) The map shows the distribution of three of these species of hare. Key Jameson's hare Smith's hare Natal rock hare (i) What is the evidence from the map that suggests that Smith’s hare and the Natal rock hare are different species? ........................................................................................................................... ........................................................................................................................... (1) (ii) Suggest what has caused the gene pools of the two populations of Jameson’s hare to differ. ........................................................................................................................... ........................................................................................................................... ........................................................................................................................... ........................................................................................................................... (2) (Total 5 marks) Sir George Monoux Sixth Form College 6 3. In cats, one of the genes for coat colour is present only on the X chromosome. This gene has two alleles. The allele for ginger fur, XB, is dominant to that for black fur, Xb (a) All the cells in the body of a female mammal carry two X chromosomes. During an early stage of development one of these becomes inactive and is not expressed. Therefore female mammals have patches of cells with one X chromosome expressed and patches of cells with the other X chromosome expressed. Tortoiseshell cats have coats with patches of ginger and patches of black fur. (i) What is the genotype of a tortoiseshell cat? ........................................................................................................................... (1) (ii) Explain why there are no male tortoiseshell cats. ........................................................................................................................... (1) (b) A cat breeder who wished to produce tortoiseshell cats crossed a black female cat with a ginger male. Complete the genetic diagram and predict the percentage of tortoiseshell kittens expected from this cross. Parental phenotypes: black female ginger male Parental genotypes: ......................... ........................ Gamete genotypes: ......................... ........................ Offspring genotypes: .................................................................................................. Percentage of tortoiseshell kittens: ............................................................................. (3) (Total 5 marks) Sir George Monoux Sixth Form College 7 4. The inheritance of the ABO blood groups is an example of multiple allele inheritance and is controlled by three alleles of a single gene, IO, IA and IB These three alleles determine the activity of an enzyme which modifies the structure of an antigen on the cell surface membrane of the red blood cells. This is summarised below. Antigen on cell surface membrane (a) I O produces inactive enzyme Antigen unchanged I A produces enzyme which adds acetylgalactosamine to antigen Antigen A I B produces enzyme which adds galactose to antigen Antigen B In terms of mutation, explain each of the following statements. (i) The alleles IA and IB differ at several nucleotide positions but produce enzymes which are very similar in their structure. (2) (ii) The IO allele has a single base deletion and gives rise to an inactive enzyme. (3) (b) Briefly explain how a DNA (gene) probe could be used to identify the presence of the 1o allele in a sample of DNA, (3) (c) The allele IO is recessive to both alleles IA and IB. Alleles IA and IB are codominant, that is, they are both expressed in the phenotype. The diagram shows the inheritance of ABO blood groups in one family. 1 2 A 3 5 4 B O AB Female 6 7 Male Sir George Monoux Sixth Form College 8 (i) Give the blood group genotype or genotypes of the sperm cells produced by individual 2. (1) (ii) Give the blood group phenotype of individual 1. (1) (iii) Calculate the probability that the next child produced by individuals 4 and 5 will be a boy with blood group A. Show your working. (2) (d) Explain why a person with blood group O: (i) can safely give blood to someone with blood of any ABO type; (2) (ii) can only safely receive blood from someone with blood group O (2) (e) (i) In a study of people living in India, the frequency of the IO allele was found to be 0.55 and that of the IA allele, 0.18. What was the frequency of the IB allele in this population? (1) (ii) Smallpox was an extremely severe disease which was particularly common among the people of the Indian sub-continent. It has been suggested that the smallpox virus had proteins on its surface which were very similar to the A antigen. Use this information to suggest why people with blood groups B and O were less likely to develop smallpox than those with blood groups A and AB. (3) (Total 20 marks) 5. In an experiment, males and females of different species of fruit fly, Drosophila, were kept together. Male fruit flies show complex courtship behaviour before they attempt to mate. The table shows the percentage of females that mated when kept with males of different species. Females Males Percentage of females that mated D. serrata D. serrata 90.2 D. serrata D. birchii 0.7 D. serrata D. dominicana 1.3 D. birchii D. birchii 76.9 D. birchii D. serrata 1.0 D. birchii D. dominicana 0.4 D. dominicana D. dominicana 93.0 D. dominicana D. serrata 0.0 D. dominicana D. birchii 3.7 Sir George Monoux Sixth Form College 9 Sir George Monoux Sixth Form College 10 (a) In the classification of fruit flies, which biological subdivision is represented by the name Drosophila? ..................................................................................................................................... (1) (b) (i) What do the data show about the mating preference of female Drosophila? ........................................................................................................................... ........................................................................................................................... (1) (ii) Suggest an explanation for this mating preference. ........................................................................................................................... ........................................................................................................................... ........................................................................................................................... ........................................................................................................................... (2) (iii) Suggest how these three species of Drosophila might have evolved from a common ancestor. ........................................................................................................................... ........................................................................................................................... ........................................................................................................................... ........................................................................................................................... (3) (Total 7 marks) 6. (a) Explain the meaning of the term gene pool. ..................................................................................................................................... ..................................................................................................................................... ..................................................................................................................................... (1) In two-spot ladybirds, the colour of the wing-cases is genetically determined. The allele for red wing-cases, R, is dominant to that for black wing-cases, r. (b) In a ladybird with black wing-cases, how many copies of the r allele would you expect to find in a nucleus taken from a muscle cell in the insect’s leg? Explain your answer. ..................................................................................................................................... ..................................................................................................................................... (1) Sir George Monoux Sixth Form College 11 (c) In a population of two-spot ladybirds found on a patch of nettles, 168 had red wing-cases and 32 had black wing-cases. Showing your working in each case, calculate the frequency of: (i) the r allele; Answer: ............................................ (2) (ii) the R allele. Answer: ............................................ (1) (Total 5 marks) 7. Answers should be written in continuous prose. Credit will be given for biological accuracy, the organisation and presentation of the information and the way in which the answer is expressed. Read the following passage Bt is a toxin made by the soil bacterium, Bacillus thuringiensis. It is very toxic to insects so it is an effective insecticide. Unfortunately, resistant strains have developed in the diamond-back moth, whose caterpillars are important pests of crops of the cabbage family. To try to overcome some of the problems of resistance, a programme of crop management was developed. Studies showed that the allele which confers resistance on diamond-back moths was recessive. Farmers were encouraged to leave a few untreated fields in which moths that were susceptible to Bt would survive. If the rest of the fields were then sprayed with Bt, a few resistant individuals would remain. However, because they were likely to mate with susceptible individuals from the untreated fields, the number of resistant moths in the population would not increase. (a) Many populations of insect pest have become resistant to insecticides. Explain how selection can result in an insect population which is resistant to a particular insecticide. ..................................................................................................................................... ..................................................................................................................................... ..................................................................................................................................... ..................................................................................................................................... ..................................................................................................................................... (5) Sir George Monoux Sixth Form College 12 (b) (i) Explain how the programme of crop management described in the second paragraph prevents the number of resistant moths from increasing. ........................................................................................................................... ........................................................................................................................... ........................................................................................................................... ........................................................................................................................... ........................................................................................................................... (ii) Explain why this programme would not work if the resistance allele were dominant. ........................................................................................................................... ........................................................................................................................... ........................................................................................................................... ........................................................................................................................... ........................................................................................................................... ........................................................................................................................... (6) (Total 11 marks) 8. In the flour beetle, the allele for red body colour (R) is dominant to the allele for black body colour (r). A mixed culture of red beetles and black beetles was kept in a container in the laboratory under optimal breeding conditions. After one year, there were 149 red beetles and 84 black beetles in the container. (a) Use the Hardy-Weinberg equation to calculate the expected percentage of heterozygous red beetles in this population. Answer: .............................................. (3) Sir George Monoux Sixth Form College 13 (b) Several assumptions are made when using the Hardy-Weinberg equation. Give two of these. 1.................................................................................................................................. 2.................................................................................................................................. (2) (Total 5 marks) 9. (a) The diagram shows an outline of the nitrogen cycle. Nitrogen gas in atmosphere Plant protein Animal protein Death and decay in soil Ammonia Nitrogen gas Process X Substance A Process Z Name: (i) substance A; ........................................................................................................................... (ii) process X; ........................................................................................................................... (iii) process Z. ........................................................................................................................... (3) Sir George Monoux Sixth Form College 14 (b) The table shows the yield of a crop when different levels of nitrogen fertiliser were applied. (i) Nitrogen fertiliser applied/ kg hectare–1 Yield/ tonnes hectare–1 0 2.8 50 3.3 100 4.2 150 4.7 200 4.7 Describe the effect that the fertiliser had on the yield of the crop. ........................................................................................................................... ........................................................................................................................... (1) (ii) Explain two disadvantages of applying nitrogen fertiliser at levels above 150 kg hectare–1. 1......................................................................................................................... ........................................................................................................................... 2......................................................................................................................... ........................................................................................................................... (4) (c) The graphs show the range of heights of samples of two varieties of wheat grown under the same conditions. Variety A is a modem form and Variety B is a form that was commonly grown 100 years ago. 200 Number of plants 200 150 Number of plants 100 50 150 100 50 0 0 50 100 Height / cm Variety A Sir George Monoux Sixth Form College 150 50 100 Height / cm 150 Variety B 15 (i) Name the type of variation shown in these two graphs. ........................................................................................................................... (1) (ii) Describe two differences shown in the graphs between Variety A and B. 1......................................................................................................................... ........................................................................................................................... 2......................................................................................................................... ........................................................................................................................... (2) (iii) Suggest how the differences between the two varieties could have been brought about. ........................................................................................................................... ........................................................................................................................... ........................................................................................................................... ........................................................................................................................... (2) (iv) Suggest the advantages that these differences could have for modern farmers. ........................................................................................................................... ........................................................................................................................... ........................................................................................................................... ........................................................................................................................... (2) Assume that two genes affect the height of wheat plants and both of these genes have two alleles. The table gives a summary of some possible genotypes and phenotypes. Genotype Phenotype height of wheat/cm AABB 100 AaBb 70 AAbb 70 aabb 40 Sir George Monoux Sixth Form College 16 A wheat plant that was 100 cm tall was crossed with a wheat plant that was 40 cm tall, fertilisation occurred and the seeds were planted and grown. (d) Using only the information in the table, answer the following questions. (i) What are the genotypes of the gametes in this cross? ........................................................................................................................... (1) (ii) What would be the expected genotype and phenotype of the resulting offspring? Genotype ........................................................................................................... Phenotype .......................................................................................................... (2) (Total 18 marks) 10. The diagram shows three generations of a family. 1 2 5 6 3 4 7 8 9 10 11 Key: Unaffected male Unaffected female Affected male Affected female No member of the family showed the symptoms of cystic fibrosis (CF) until the son was born in the third generation. A single gene is responsible for the inheritance of cystic fibrosis. (a) Assume that no gene mutations have occurred in these generations. Use F for the dominant allele and f for the recessive allele to give the possible genotype or genotypes of: individual 7;................................................................................................................. individual 11................................................................................................................ (2) Sir George Monoux Sixth Form College 17 (b) Give the probability that the next child of parents 7 and 8 will be a girl with cystic fibrosis. Show how you arrived at your answer. Probability that child will be a girl with cystic fibrosis: ............................................ (2) (c) Attempts to treat cystic fibrosis using gene therapy have used viruses as vectors. The viruses are introduced into the lungs using aerosols. (i) Explain why viruses are useful as vectors. .......................................................................................................................... .......................................................................................................................... (1) (ii) Suggest a reason why gene therapy for the treatment of cystic fibrosis has not yet been very successful. .......................................................................................................................... .......................................................................................................................... (1) (d) In the UK, 1 in every 2 500 children has cystic fibrosis. What is the frequency of the cystic fibrosis allele in children in the UK? Show how you arrived at your answer. Frequency of cystic fibrosis allele: ........................... (2) (Total 8 marks) Sir George Monoux Sixth Form College 18 11. In cats, some aspects of the inheritance of fur colour are sex linked. When a ginger male cat was crossed with a black female, all the female kittens were tortoiseshell (a pattern of black hairs and ginger hairs) and all the male kittens were black. However, in the reciprocal cross, although all the female kittens were again tortoiseshell, the male kittens were ginger. (a) Complete the following genetic diagrams to explain the results of these two crosses. Use the following symbols: XB = an X-chromosome carrying an allele for black hair. XG = an X-chromosome carrying an allele for ginger hair. Cross 1 Cross 2 Parental phenotypes Ginger x male Black female Black male x Ginger female Parental genotypes .......... .......... .......... .......... Gametes ................... ................... ................... ................... Offspring genotypes ........................................ ........................................ Offspring phenotypes ....................................... ....................................... ....................................... ....................................... (4) (b) Why were no male tortoiseshell cats produced in these crosses? ..................................................................................................................................... ..................................................................................................................................... (1) (Total 5 marks) Sir George Monoux Sixth Form College 19 12. Read the following passage. In the living world, success may be measured by reproductive capacity. But this brings its own problems: the more individuals there are, the greater the competition and struggle for survival. 5 10 15 In the early 1830s, Charles Darwin visited the Galapagos Islands, some 1000 km off the coast of Ecuador, where he discovered several different species of small birds, called ground finches. They all seemed to be related to similar birds found on the South American mainland and Darwin suggested that they might therefore have originated from a common ancestor and changed over the years to their present form. More recently, measurements have shown that there are variations, not only between, but also within each species. For instance, on one of the larger islands, called Albemarle, two species of ground finch share the same habitat. The beaks of one species, Geospiza fortis, range in depth from 11 to 16 mm, while the other, Geospiza fuliginosa, possesses beaks varying from 7 to 10 mm. On another island, G. fuliginosa is absent and here G. fortis has a range of beak depths from 9 to 12mm. What causes this divergence when living together? Perhaps competition is the answer. The two species specialised by feeding on different-sized seeds. As beak depths diverged, competition was reduced. Use information from the passage and your own knowledge to answer the following question. Explain how the process of natural selection on the two islands might have led to the different ranges of beak depth in G. fortis. ............................................................................................................................................... ............................................................................................................................................... ............................................................................................................................................... ............................................................................................................................................... ............................................................................................................................................... ............................................................................................................................................... ............................................................................................................................................... ............................................................................................................................................... (Total 7 marks) 13. In tomato plants, the genes for flower colour and for height are on different chromosomes. The allele for yellow flowers (Y) is dominant to that for white flowers (y) and the allele for tall plants (T) is dominant to that for dwarf plants (t). A tall tomato plant with yellow flowers was pollinated with pollen from a dwarf plant with white flowers. The resulting seeds were planted and grew into plants with the following phenotypes: Tall, yellow: 63 Dwarf, yellow: 58 Sir George Monoux Sixth Form College 20 (a) (i) To what Mendelian ratio do these results approximate? .......................................................................................................................... (1) (ii) Explain why the results of crosses like this only approximate to the expected Mendelian ratio. .......................................................................................................................... .......................................................................................................................... (1) (b) Use a genetic diagram to explain the results of this cross. (3) (Total 5 marks) 14. Huntington’s disease is a human inherited condition resulting in gradual degeneration of nerve cells in the brain. It is caused by a dominant allele but usually no symptoms are evident until the person is at least 30 years old. It is very rare in most populations. However, in one isolated area in Venezuela, 48% of the population possess a genotype which gives rise to Huntington’s disease. Many of the inhabitants of this area can trace their origins back to a common ancestor 200 years ago. (a) Use the Hardy-Weinberg equation to estimate the percentage of this Venezuelan population which is heterozygous for Huntington’s disease. Show your working. Answer = ....................................... % (3) Sir George Monoux Sixth Form College 21 (b) Suggest why (i) there is such a high incidence of Huntington’s disease in this population; .......................................................................................................................... .......................................................................................................................... .......................................................................................................................... (ii) Huntington’s disease has not been eliminated from this population by natural selection. .......................................................................................................................... .......................................................................................................................... .......................................................................................................................... (3) (Total 6 marks) 15. New Zealand beech trees do not produce seeds every year. A study was carried out on the mice living in an isolated New Zealand beech forest. Because of the location of this forest, biologists could only visit it at monthly intervals and stay approximately 12 hours on each visit. At the beginning of each visit, they set all the traps they had available. This number varied. At the end of the visit, they collected the traps and released any mice they had captured. Figure 1 shows the population density of the mice at different times during a New Zealand beech seed year and a non-seed year. New Zealand beech seed year 25 Number 20 of mice captured 15 per 100 10 traps Non-seed year 5 0 May Aug Nov Month Feb May Figure 1 Sir George Monoux Sixth Form College 22 (a) Use the information in the question to suggest (i) why the mark-release-recapture method would have given unreliable results; .......................................................................................................................... .......................................................................................................................... .......................................................................................................................... .......................................................................................................................... (2) (ii) the advantage of giving the number of mice captured per 100 traps rather than just the number of mice captured. .......................................................................................................................... .......................................................................................................................... .......................................................................................................................... .......................................................................................................................... (2) (b) (i) A statistical test was carried out on the August figures. The population density of mice in the seed year was found to be significantly different at the p = 0.05 level from the population density in the non-seed year. Explain the meaning of this statement. .......................................................................................................................... .......................................................................................................................... .......................................................................................................................... .......................................................................................................................... (2) (ii) Suggest why the population density increases in a seed year. .......................................................................................................................... .......................................................................................................................... .......................................................................................................................... .......................................................................................................................... (2) Sir George Monoux Sixth Form College 23 In a different survey, mice were trapped at various sites in the UK. Figure 2 shows the mean body mass and the standard deviation of the adult males that were among the trapped mice. Refrigerated cold stores Farms in Scotland Farms in Wales Farms in Northern England 12 14 16 18 20 Mass / g 22 24 26 Figure 2 (c) (i) Explain why the data for only the male mice were plotted in Figure 2. .......................................................................................................................... .......................................................................................................................... (1) (ii) In collecting the raw data in this survey, the investigators also measured the amount of tooth wear shown by the mice. Suggest why. .......................................................................................................................... .......................................................................................................................... .......................................................................................................................... .......................................................................................................................... (2) (d) (i) Explain the advantage of a large body mass to mice living in a refrigerated cold store. .......................................................................................................................... .......................................................................................................................... .......................................................................................................................... .......................................................................................................................... (2) Sir George Monoux Sixth Form College 24 (ii) Use the information in Figure 2 to explain what is meant by directional selection. .......................................................................................................................... .......................................................................................................................... .......................................................................................................................... .......................................................................................................................... .......................................................................................................................... .......................................................................................................................... (3) (e) The colour of wild mice is grey but in some island populations there are black mice. The difference in colour is caused by a single pair of alleles. (i) Describe how you could use genetic crosses to show that the allele for black is the recessive allele. .......................................................................................................................... .......................................................................................................................... .......................................................................................................................... .......................................................................................................................... (2) (ii) Explain how you could find the frequency of the recessive allele in a population of mice living on an island. .......................................................................................................................... .......................................................................................................................... .......................................................................................................................... .......................................................................................................................... (2) (Total 20 marks) 16. Read the following passage. Despite its bad press, cholesterol is essential. We cannot manage without it. It is an important component of plasma membranes. Myelin, the substance surrounding many nerve fibres, is involved in the rapid conduction of nerve impulses and myelin is rich in cholesterol. 5 Being insoluble in water, cholesterol cannot be transported in solution in the blood plasma. Instead, it is packaged in lipoprotein particles. The main carrier of cholesterol is low-density lipoprotein (LDL). Each LDL particle has a cholesterol core protected by an outer coat and topped by a special protein molecule. Sir George Monoux Sixth Form College 25 10 15 20 How is LDL-packaged cholesterol taken up by cells? Plasma membranes are studded with binding sites for this "topping" protein. These LDL receptors are made of protein with some sugar chains attached, and their numbers increase or decrease according to the cell's needs for cholesterol. After latching on to LDL receptors, LDL particles are pulled into the cytoplasm and processed in various ways. This regulatory mechanism, however, cannot control cholesterol concentrations outside cells when large amounts of cholesterol are present in the blood. The excess cholesterol is eventually deposited in artery walls. This leads to an increased risk of thrombosis. In the 1980s, researchers purified the LDL receptor molecule and determined the sequence of its 839 amino acids. They also isolated the LDL receptor gene. Mutation of this gene gives rise to a condition known as familial hypercholesterolemia (FH). All the evidence we have, such as that all affected individuals have at least one affected parent, and that male to male transmission is possible, indicates that the mutant allele is dominant and located on one of the autosomes. The FH allele is found in a high frequency in some populations. Among South African Afrikaners, for example, 1 in 100 are FH heterozygotes while 1 in 30 000 are homozygous for the FH allele. These people are all at risk of premature death from coronary heart disease. Source: adapted from MANGE and MANGE, Basic Human Genetics (Sinaeur Associates Inc.) 1994 Use information from the passage and your own knowledge to answer the following questions. (a) Explain how myelin is involved in the rapid conduction of nerve impulses (lines 2-3). ..................................................................................................................................... ..................................................................................................................................... ..................................................................................................................................... ..................................................................................................................................... (2) (b) Describe how negative feedback is involved in controlling the concentration of cholesterol in the cytoplasm of a cell. ..................................................................................................................................... ..................................................................................................................................... ..................................................................................................................................... ..................................................................................................................................... (3) (c) (i) Explain how a mutation of the LDL receptor gene can lead to a high concentration of cholesterol in the blood. .......................................................................................................................... .......................................................................................................................... .......................................................................................................................... .......................................................................................................................... (2) Sir George Monoux Sixth Form College 26 (ii) Describe how excess cholesterol deposited in artery walls can lead to an increased risk of thrombosis (lines 14-15). .......................................................................................................................... .......................................................................................................................... .......................................................................................................................... .......................................................................................................................... (2) (d) What is the minimum number of nucleotides in the mRNA molecule that codes for the LDL receptor? Explain how you arrived at your answer. ..................................................................................................................................... ..................................................................................................................................... (1) (e) All individuals affected with FH have at least one affected parent (line 19). Explain how this shows that the FH allele is not recessive to the normal allele. ..................................................................................................................................... ..................................................................................................................................... ..................................................................................................................................... ..................................................................................................................................... (2) (f) Use the data in the last paragraph to estimate the number of people in the South African Afrikaner population at risk from premature death from coronary heart disease because of FH. Give your answer per 100 000 of the population. Show your working. Answer .................................... per 100 000 (3) (Total 15 marks) 17. In humans, cystic fibrosis is caused by a recessive allele, f. (a) What is an allele? ..................................................................................................................................... ..................................................................................................................................... (1) Sir George Monoux Sixth Form College 27 (b) A man and woman are both heterozygous for the cystic fibrosis allele. They have one healthy son but would like to have another child. ‘What is the probability that they will produce a girl who has cystic fibrosis? Show your working. Probability = ......................................... (2) (Total 3 marks) 18. (a) What is meant by reproductive isolation? ..................................................................................................................................... ..................................................................................................................................... ..................................................................................................................................... (1) (b) Explain how geographical isolation can lead to the formation of new species. ..................................................................................................................................... ..................................................................................................................................... ..................................................................................................................................... ..................................................................................................................................... ..................................................................................................................................... ..................................................................................................................................... ..................................................................................................................................... ..................................................................................................................................... (4) (Total 5 marks) Sir George Monoux Sixth Form College 28 19. The inheritance of body colour in fruit flies was investigated. Two fruit flies with grey bodies were crossed. Of the offspring, 152 had grey bodies and 48 had black bodies. (a) Using suitable symbols, give the genotypes of the parents. Explain your answer. Genotypes .................................................................................................................. Explanation ................................................................................................................ ..................................................................................................................................... ..................................................................................................................................... ..................................................................................................................................... (2) (b) (i) Explain why a statistical test should be applied to the data obtained in this investigation. ........................................................................................................................... ........................................................................................................................... ........................................................................................................................... ........................................................................................................................... (2) (ii) The null hypothesis in this investigation predicted that there would be no difference between the observed and expected values. Use the table to determine whether this hypothesis can be supported. Explain how you arrived at your answer. Degrees of freedom Probability value 0.99 9.95 0.1 0.05 0.01 0.001 1 0.0002 0.0039 2.71 3.84 6.63 10.83 2 0.020 0.103 4.61 5.99 9.21 13.82 3 0.115 0.352 6.25 7.81 11.34 16.27 4 0.297 0.711 7.78 9.49 13.28 18.47 ........................................................................................................................... ........................................................................................................................... ........................................................................................................................... ........................................................................................................................... (2) Sir George Monoux Sixth Form College 29 (c) A species of insect, only found on a remote island, has a characteristic controlled by a pair of codominant alleles, CM and CN. (i) What is meant by codominant? ........................................................................................................................... ........................................................................................................................... (1) (ii) There were 500 insects in the total population. In this population, 300 insects had the genotype CM CM, 150 had the genotype CM CN and 50 had the genotype CN CN. Calculate the actual frequency of the allele CN by using these figures. Show your working. Answer ........................................ (2) (iii) Use your answer to (c) (ii) and the Hardy-Weinberg equation to calculate the number of insects that would be expected to have the genotype CN CN. Answer ........................................ (3) (Total 12 marks) Sir George Monoux Sixth Form College 30 20. (a) Caterpillars were fed on diets in which different amino acids were absent. Figure 1 shows the percentage of caterpillars which survived on these diets for 20 days. 100 80 Percentage of 60 caterpillars surviving for 20 days 40 20 0 Control group Valine Leucine Proline Glutamate Amino acid absent from diet Figure 1 (i) Describe how the control group of caterpillars should have been treated. ........................................................................................................................... ........................................................................................................................... ........................................................................................................................... ........................................................................................................................... (2) (ii) In caterpillars, glutamate is a non-essential amino acid. Explain the evidence from Figure 1 which supports this. ........................................................................................................................... ........................................................................................................................... ........................................................................................................................... ........................................................................................................................... (2) Sir George Monoux Sixth Form College 31 The rate of uptake of amino acids by the epithelial cells lining a piece of rat small intestine was investigated. Two experiments were carried out. In experiment A, the contents of the intestine were stirred while the measurements were taken. In experiment B, the contents of the intestine were not stirred. The table shows the results of these experiments. (b) Concentration of amino acids in intestine/ mmol dm –3 A. Contents stirred 0 0 0 2 5.1 2.9 4 7.8 5.6 6 9.4 6.5 8 10.8 7.2 10 11.1 7.5 (i) Rate of uptake of amino acids / arbitrary units B. Contents not stirred In experiment B, describe how the rate of uptake changes as the concentration of amino acids in the intestine increases. ........................................................................................................................... ........................................................................................................................... ........................................................................................................................... ........................................................................................................................... (2) (ii) It has been suggested that carrier proteins are involved in transporting amino acids from the intestine. Explain how the results of experiment B support this suggestion. ........................................................................................................................... ........................................................................................................................... ........................................................................................................................... ........................................................................................................................... (2) (c) (i) Explain how mixing the intestine contents increases the rate of absorption of amino acids. ........................................................................................................................... ........................................................................................................................... ........................................................................................................................... ........................................................................................................................... (2) (ii) Which tissue, present in the wall of the intestine, mixes the contents of the intestine in a live animal? Sir George Monoux Sixth Form College 32 ........................................................................................................................... (1) Sir George Monoux Sixth Form College 33 Figure 2 shows some biochemical pathways involving the amino acid phenylalanine in the human body. From protein in diet Phenylalanine hydroxylase Phenylalanine H H N H C Tyrosine O H OH H C H N CH 2 C O C OH CH 2 OH Phenyl pyruvic acid and other substances Thyroid hormone DOPA Melanin Dopamine (Brain neurotransmitter) Causes damage to growing brain Noradrenaline and adrenaline Figure 2 (d) Explain why the enzyme which converts phenylalanine into tyrosine is called phenylalanine hydroxylase. ..................................................................................................................................... ..................................................................................................................................... (1) (e) Phenylketonuria is a genetic disease in which the enzyme phenylalanine hydroxylase (PAH) is missing. If untreated, phenylketonuria causes damage to the growing brain. Suggest and explain one other sign or symptom of phenylketonuria. ..................................................................................................................................... ..................................................................................................................................... ..................................................................................................................................... ..................................................................................................................................... ..................................................................................................................................... ..................................................................................................................................... (3) Sir George Monoux Sixth Form College 34 (f) Babies who are diagnosed as having phenylketonuria are fed on a special diet that contains only small amounts of phenylalanine and extra tyrosine. This special diet is necessary only until the child reaches the age of about 6 years. After this a normal but low-protein diet is recommended. (i) Explain why the special diet contains extra tyrosine. ........................................................................................................................... ........................................................................................................................... ........................................................................................................................... ........................................................................................................................... (2) (ii) Explain why the special diet is only necessary until the child reaches the age of about 6 years. ........................................................................................................................... ........................................................................................................................... (1) (g) A woman who has phenylketonuria may have a child who does not have this condition. It is important that a woman with phenylketonuria keeps to the special diet throughout her pregnancy, otherwise her child will be born with brain damage. Explain why. ..................................................................................................................................... ..................................................................................................................................... ..................................................................................................................................... ..................................................................................................................................... (2) (Total 20 marks) 21. In the squirting cucumber, there are three kinds of plants; plants with male flowers only, plants with female flowers only, and hermaphrodite plants with both male and female flowers. Sex is determined by a single gene with three alleles. AD is the allele for male. It is dominant over the other two alleles. A+ is the allele for hermaphrodite. It is dominant over allele Ad. Ad is the allele for female. It is recessive to the other two alleles. (a) (i) Give the genotype of a female squirting cucumber. .............................................................................................................................. (1) Sir George Monoux Sixth Form College 35 (ii) Explain why a male squirting cucumber cannot have the genotype ADAD. .............................................................................................................................. .............................................................................................................................. .............................................................................................................................. .............................................................................................................................. (2) (b) Complete the genetic diagram to show how it would be possible for a cross between two hermaphrodite plants to produce female offspring. Parent phenotypes: Parent genotypes: hermaphrodite × hermaphrodite Gametes: Offspring genotypes: (2) (Total 5 marks) 22. (a) Explain what is meant by a gene pool. ........................................................................................................................................... ........................................................................................................................................... ........................................................................................................................................... ........................................................................................................................................... (2) Sir George Monoux Sixth Form College 36 (b) Greater willow herb is a common plant found in damp places. It usually has red flowers controlled by the allele R. Plants with the genotype rr, however, have white flowers. In a sample of plants growing beside a ditch, 17 had white flowers and 327 had red flowers. (i) Calculate the frequency of the r allele in this sample. Show your working. Frequency of r allele = ....................................................... (2) (ii) The Hardy-Weinberg equation could be used to find the frequencies of the different genotypes in the population from which this sample was taken. Give one assumption that must be made if the equation is to be applied. .............................................................................................................................. .............................................................................................................................. (1) (Total 5 marks) 23. Cyanide is a poisonous substance. Cyanogenic clover plants produce cyanide when their tissues are damaged. The ability to produce cyanide is controlled by genes at loci on two different chromosomes. The dominant allele, A, of one gene controls the production of an enzyme which converts a precursor to linamarin. The dominant allele, L, of the second gene controls the production of an enzyme which converts linamarin to cyanide. This is summarised in the diagram. Allele A Allele L Enzyme A Enzyme L Precursor (a) Linamarin Cyanide Acyanogenic clover plants cannot produce cyanide. Explain why a plant with the genotype aaLl cannot produce cyanide. ........................................................................................................................................... ........................................................................................................................................... (1) (b) A clover plant has the genotype AaLl. (i) Give the genotypes of the male gametes which this plant can produce. .............................................................................................................................. (1) Sir George Monoux Sixth Form College 37 (ii) Explain how meiosis results in this plant producing gametes with these genotypes. .............................................................................................................................. .............................................................................................................................. .............................................................................................................................. .............................................................................................................................. (2) (c) Two plants, heterozygous for both of these pairs of alleles, were crossed. What proportion of the plants produced from this cross would you expect to be acyanogenic but able to produce linamarin? Use a genetic diagram to explain your answer. (3) In an investigation, cyanogenic and acyanogenic plants were grown together in pots. Slugs were placed in each pot and records were kept of the number of leaves damaged by the feeding of the slugs over a period of 7 days. The results are shown in the table. (d) Undamaged Damaged Cyanogenic 160 120 Acyanogenic 88 192 A 2 test was carried out on the results. (i) Suggest the null hypothesis that was tested. .............................................................................................................................. .............................................................................................................................. (1) Sir George Monoux Sixth Form College 38 (ii) 2 was calculated. When this value was looked up in a table, it was found to correspond to a probability of less than 0.05. What conclusion can you draw from this? .............................................................................................................................. .............................................................................................................................. .............................................................................................................................. .............................................................................................................................. .............................................................................................................................. .............................................................................................................................. (3) A second investigation was carried out in a field of grass which had been undisturbed for many years. The table shows the population density of slugs and the numbers of cyanogenic and acyanogenic clover plants at various places in the field. Population density of slugs Number of acyanogenic clover plants per m2 Number of cyanogenic clover plants per m2 Very low 26 10 Low 17 26 High 0 10 Very High 0 5 (e) Explain the proportions of the two types of clover plant in different parts of the field. ........................................................................................................................................... ........................................................................................................................................... ........................................................................................................................................... ........................................................................................................................................... ........................................................................................................................................... ........................................................................................................................................... ........................................................................................................................................... ........................................................................................................................................... (4) (Total 15 marks) Sir George Monoux Sixth Form College 39 24. Duchenne muscular dystrophy is a sex-linked inherited condition which causes degeneration of muscle tissue. It is caused by a recessive allele. The diagram shows the inheritance of muscular dystrophy in one family. 1 3 4 10 11 5 2 6 7 8 12 9 13 14 15 Key: = male with muscular dystrophy = unaffected male = female with muscular dystrophy = unaffected female (a) Give evidence from the diagram which suggests that muscular dystrophy is (i) sex-linked; .................................................................................................................. ..................................................................................................................................... (1) (ii) caused by a recessive allele. ....................................................................................... ..................................................................................................................................... (1) Sir George Monoux Sixth Form College 40 (b) Using the following symbols, XD = an X chromosome carrying the normal allele Xd = an X chromosome carrying the allele for muscular dystrophy Y = a Y chromosome give all the possible genotypes of each of the following persons. 5 ..................................................................................................................................... 6 ..................................................................................................................................... 7 ..................................................................................................................................... 8 ..................................................................................................................................... (2) (c) A blood test shows that person 14 is a carrier of muscular dystrophy. Person 15 has recently married person 14 but as yet they have had no children. What is the probability that their first child will be a male who develops muscular dystrophy? ..................................................................................................................................... (1) (Total 5 marks) 25. Warfarin is a substance which inhibits blood clotting. Rats which eat warfarin are killed due to internal bleeding. Some rats are resistant to warfarin as they have the allele WR. Rats have three possible genotypes: WRWR resistant to warfarin WRWS resistant to warfarin WSWS susceptible (not resistant) to warfarin. In addition, rats with the genotype WRWR require very large amounts of vitamin K in their diets. If they do not receive this they will die within a few days due to internal bleeding. (a) How can resistance suddenly appear in an isolated population of rats which has never before been exposed to warfarin? ..............................................................................................................…..................... ..............................................................................................................…..................... (1) Sir George Monoux Sixth Form College 41 (b) A population of 240 rats was reared in a laboratory. They were all fed on a diet containing an adequate amount of vitamin K. In this population, 8 rats had the genotype WSWS, 176 had the genotype WRWS and 56 had the genotype WRWR. (i) Use these figures to calculate the actual frequency of the allele WR in this population. Show your working. Answer .................................. (2) (ii) The diet of the rats was then changed to include only a small amount of vitamin K. The rats were also given warfarin. How many rats out of the population of 240 would be likely to die within a few days? ............................................................................................................................ (1) (c) In a population of wild rats, 51% were resistant to warfarin. (i) Use the Hardy-Weinberg equation to estimate the percentage of rats in this population which would be heterozygous for warfarin resistance. Show your working. Answer ....................................... % (3) (ii) If all the susceptible rats in this population were killed by warfarin, more susceptible rats would appear in the next generation. Use a genetic diagram to explain how. Sir George Monoux Sixth Form College 42 (2) Sir George Monoux Sixth Form College 43 (iii) The graph shows the change in the frequency of the WS allele in an area in which warfarin was regularly used. Describe and explain the shape of the curve. Frequency of W S allele Time ......................................……….......................................................................... ............................................................................................................................ ............................................................................................................................ ............................................................................................................................ ............................................................................................................................ ............................................................................................................................ ............................................................................................................................ ............................................................................................................................ (4) (iv) Give two assumptions that must be made when using the Hardy-Weinberg equation. 1 ......................................................................................................................... ............................................................................................................................ 2 ......................................................................................................................... ............................................................................................................................ (2) (Total 15 marks) Sir George Monoux Sixth Form College 44 26. In fruit flies, the allele for grey body, G, is dominant to the allele for ebony body, g, and the allele for normal wings, N, is dominant to the allele for vestigial wings, n. Vestigial-winged flies, heterozygous for grey body colour, were crossed with ebony-bodied flies, heterozygous for normal wings. Complete the genetic diagram to show the genotypes and phenotypes in this cross. Parental phenotypes Grey body, vestigial wings Ebony body, normal wings Parental genotypes .............................. ............................... Gamete genotypes .............................. ............................... Offspring genotypes ............................................................................................................ Offspring phenotypes .......................................................................................................... (Total 4 marks) 27. (a) Explain the meaning of these ecological terms. Population .….............................................................................................................. ............……….............................................................................................................. Community ............……….......................................................................................... ............……….............................................................................................................. (2) Sir George Monoux Sixth Form College 45 (b) Some students used the mark-release-recapture technique to estimate the size of a population of woodlice. They collected 77 woodlice and marked them before releasing them back into the same area. Later they collected 96 woodlice, 11 of which were marked. (i) Give two conditions necessary for results from mark-release-recapture investigations to be valid. 1 ........................................................................................................................ ........................................................................................................................... 2 ........................................................................................................................ ........................................................................................................................... (2) (ii) Calculate the number of woodlice in the area under investigation. Show your working. Answer ...................................................... (2) (c) Explain how you would use a quadrat to estimate the number of dandelion plants in a field measuring 100 m by 150 m. ............……….............................................................................................................. ............……….............................................................................................................. ............……….............................................................................................................. ............……….............................................................................................................. ............……….............................................................................................................. ............……….............................................................................................................. (3) Sir George Monoux Sixth Form College 46 (d) Two similar species of birds (species A and species B) feed on slightly different sized insects and have slightly different temperature preferences. The diagram represents the response of each species to these factors. Tolerance of individuals of each species 2 1 Species A Temperature 5 Species B 3 4 Number of prey items eaten by individuals of each species Species B Species A Size of food item (i) Which of the numbered boxes describes conditions which represent the niche of species A; ................ the niche of species B; ................ insects too small for species B and temperature too warm for species A; ................ insects too large for species A and temperature too cool for species B? ................. (2) Sir George Monoux Sixth Form College 47 (ii) These two species are thought to have evolved as a result of sympatric speciation. Suggest how this might have occurred. ........................................................................................................................... ........................................................................................................................... ........................................................................................................................... ........................................................................................................................... ........................................................................................................................... ........................................................................................................................... ........................................................................................................................... (4) (Total 15 marks) 28. (a) Explain what is meant by stabilising selection and describe the circumstances under which it takes place. ............……….............................................................................................................. ............……….............................................................................................................. ............……….............................................................................................................. ............……….............................................................................................................. ............……….............................................................................................................. ............……….............................................................................................................. ............……….............................................................................................................. ............……….............................................................................................................. ............……….............................................................................................................. (5) Sir George Monoux Sixth Form College 48 (b) Some European clover plants can produce cyanide. Those plants that can produce cyanide are called cyanogenic; those that cannot produce cyanide are called acyanogenic. Cyanide is toxic to the cells of animals and plants. When the leaves of cyanogenic plants are damaged by slugs, or exposed to low temperatures, membranes within the cells are broken. This causes the release of the enzymes that control the reactions which produce cyanide. The proportions of cyanogenic and acyanogenic plants in clover populations were determined in different parts of Europe. These are shown in the diagram below, together with the mean minimum winter temperatures. Slugs are not usually active at temperatures below 0 °C. –4 °C 0 °C 4 °C 10 °C Key Cyanogenic plants Acyanogenic plants Population of clover plants Sir George Monoux Sixth Form College 49 Explain the proportions of cyanogenic and acyanogenic plants in clover populations growing in the area where the mean minimum winter temperature is below –4°C and in the area where it is above 10 °C. ..................................................................................................................................... ..................................................................................................................................... ..................................................................................................................................... ..................................................................................................................................... ..................................................................................................................................... ..................................................................................................................................... ..................................................................................................................................... ..................................................................................................................................... ..................................................................................................................................... (5) (Total 10 marks) 29. Human ABO blood groups are determined by the presence or absence of two antigens (A and B) on the plasma membrane of the red blood cells. The inheritance of these blood groups is controlled by three alleles: IA – determines the production of antigen A IB – determines the production of antigen B Io – determines the production of no antigen Alleles I A and I B are codominant. Allele I o is recessive to both. The pedigree shows the pattern of inheritance of these blood groups in a family over three generations. B 4 A 3 A 1 B 2 AB 5 A 6 B 7 A AB AB B O 9 10 11 12 13 Sir George Monoux Sixth Form College A 8 50 (a) (i) How many antigen-determining alleles will be present in a white blood cell? Give a reason for your answer. ........................................................................................................................... ........................................................................................................................... (1) (ii) Which antigen or antigens will be present on the plasma membranes of red blood cells of individual 5? ........................................................................................................................... (1) (b) If individuals 6 and 7 were to have another child, what is the probability that this child would be male and blood group A? Explain your answer. ..................................................................................................................................... ..................................................................................................................................... ..................................................................................................................................... ..................................................................................................................................... ..................................................................................................................................... ..................................................................................................................................... (3) (Total 5 marks) 30. (a) Some antibiotics bind with specific receptors in the plasma membranes of bacteria. The structure of these receptors is determined genetically. Bacteria can become resistant to an antibiotic because a gene mutation results in an altered receptor. Explain how resistance to an antibiotic could become widespread in a bacterial population following a gene mutation conferring resistance in just one bacterium. ..................................................................................................................................... ..................................................................................................................................... ..................................................................................................................................... ..................................................................................................................................... ..................................................................................................................................... ..................................................................................................................................... ..................................................................................................................................... ..................................................................................................................................... ..................................................................................................................................... ..................................................................................................................................... Sir George Monoux Sixth Form College 51 (5) Sir George Monoux Sixth Form College 52 (b) Some humans have a genetic resistance to infection. A recessive allele gives increased resistance to infection by the malarial parasite. In a population, the proportion of babies born who are homozygous for this allele is 0.01. Use the Hardy-Weinberg equation to calculate the expected proportion of heterozygotes in this population. Show your working. Answer ............................................ (4) (Total 9 marks) 31. Chickens have a structure on their heads called a comb. The diagram shows four types of comb: walnut, pea, rose and single. Two genes control the type of comb; each gene has a dominant and a recessive allele. The two genes are inherited independently, but interact to produce the four types of comb. Sir George Monoux Sixth Form College Genotype Phenotype A- B- Walnut A- bb Pea aa B- Rose aa bb Single 53 The symbol - indicates that either the dominant allele or recessive allele could be present Sir George Monoux Sixth Form College 54 (a) A male with a pea comb, heterozygous for gene A, was crossed with a rose-combed female, heterozygous for gene B. Complete the genetic diagram to show the offspring expected from this cross. Phenotypes of parents Pea comb Rose comb Genotypes of parents ……………… ……………… Gametes formed ……………… ……………… Offspring genotypes ………………………………………… Ratio of offspring phenotypes ………………………………………… …………………………………………. (3) (b) Chickens with rose or single combs made up 36% of one population. Assuming the conditions of the Hardy-Weinberg equilibrium apply, calculate the frequency of allele a in this population. Show how you arrived at your answer. Frequency of allele a = ...................................... (2) (Total 5 marks) Sir George Monoux Sixth Form College 55 32. There is evidence that the first photosynthetic organisms were primitive water-dwelling bacteria. The very first of these lived near the surface of the water in lakes and contained a purple pigment that absorbed light most strongly in the green region of the spectrum. Later, other bacteria evolved that lived on the top of sediment at the bottom of the lakes (Figure 1). Gene mutations had enabled these bacteria to synthesise chlorophyll instead of the purple pigment present in the bacteria living near to the surface. Chlorophyll absorbs light most strongly in the blue and red regions of the spectrum (Figure 2). Figure 1 Light energy First bacteria lived near the surface of the water Later bacteria lived on top of the sediment at the bottom of the lake Figure 2 Pigment from surface-dwelling bacteria Chlorophyll from sediment-dwelling bacteria Absorbtion 400 Blue 500 Green 600 Red 700 Wavelength of light Sir George Monoux Sixth Form College 56 (a) Describe how light energy absorbed by chlorophyll molecules is used to synthesise ATP. ..................................................................................................................................... ..................................................................................................................................... ..................................................................................................................................... ..................................................................................................................................... ..................................................................................................................................... ..................................................................................................................................... ..................................................................................................................................... ..................................................................................................................................... ..................................................................................................................................... ..................................................................................................................................... (5) (b) Use Figure 2 to explain how natural selection would favour the evolution of sediment-dwelling bacteria containing a different photosynthetic pigment from those living near the surface of the water. ..................................................................................................................................... ..................................................................................................................................... ..................................................................................................................................... ..................................................................................................................................... ..................................................................................................................................... ..................................................................................................................................... ..................................................................................................................................... ..................................................................................................................................... ..................................................................................................................................... ..................................................................................................................................... ..................................................................................................................................... (6) (Total 11 marks) Sir George Monoux Sixth Form College 57 33. Finches are small birds. Fourteen species of finch are found on the Galapagos Islands. (a) What is a species? ..................................................................................................................................... ..................................................................................................................................... ..................................................................................................................................... ..................................................................................................................................... (2) (b) Measurements were made of the beak depth of two species of finch (species A and species B) on different islands. Species A is found on island 1, species B is found on island 2. Both species are found on island 3. They are thought to have colonised island 3 from islands 1 and 2 respectively. The graphs show the ranges of beak depths of the two species on the different islands. Species A on island 1 40 Percentage of population 20 0 7 8 9 10 11 12 13 14 15 16 Beak depth / mm Species B on island 21 40 Percentage of population 20 0 7 8 9 10 11 12 13 14 15 16 Beak depth / mm 60 Species A and B on island 3 40 Percentage of population Species B Species A 20 0 7 8 9 10 11 12 13 14 15 16 Beak depth / mm Sir George Monoux Sixth Form College 58 What type of natural selection took place in the populations of both species after they had colonised island 3? Explain your answer. ..................................................................................................................................... ..................................................................................................................................... ..................................................................................................................................... ..................................................................................................................................... ..................................................................................................................................... ..................................................................................................................................... (3) (Total 5 marks) 34.S Red-green colour blindness is caused by a mutation in the gene coding for one of the opsin proteins which are needed for colour vision. The diagram shows the inheritance of red-green colour blindness in one family. 1 5 2 6 3 7 10 8 11 4 9 12 14 13 15 16 Key = colour-blind male = unaffected male = unaffected female Sir George Monoux Sixth Form College 59 Person 12 is pregnant with her fourth child. What is the probability that this child will be a male with red-green colour blindness? Explain your answer by drawing a genetic diagram. Use the following symbols XR = an X chromosome carrying an allele for normal colour vision Xr= an X chromosome carrying an allele for red-green colour blindness Y = a Y chromosome Probability = ...................................... (Total 4 marks) 35. The inheritance of ABO blood groups is controlled by three alleles of the same gene, IA IB and IO. The alleles IA and IB are codominant. Both IA and IB are dominant to the allele IO. (a) Explain what is meant by an allele. .................................................................................................................................... .................................................................................................................................... (1) Sir George Monoux Sixth Form College 60 (b) (i) Complete the table to show the missing genotypes. Blood group phenotype Possible genotype A IAIA, .......... B IBIB, .......... AB ...................... O ...................... (2) (ii) Children of blood groups A and O were born to parents of blood groups A and B. Complete the genetic diagram to show the possible ABO blood group phenotypes of the children which could be produced from these parents. Parental phenotypes Blood group A Blood group B Parental genotypes Genotypes of gametes Genotypes of children Phenotypes of children (3) (Total 6 mark) Sir George Monoux Sixth Form College 61 36. The fruit fly is a useful animal for studying genetic crosses. The diagram shows the life cycle of the fruit fly. Male Female Mating occurs and female lays fertilised eggs 24 hours after emerging. Adult (2 mm) Sperm Egg Fertilised egg (0.5 mm) Single female lays between 80 and 200 eggs. Egg hatches into larva about one day after laying Larva (4.5 mm) Larva moults twice and changes into pupa about 6 days after laying. Adult fly emerges from pupa about 10 days after laying. (a) Pupa (3 mm) Using information from the diagram explain three ways in which the fruit fly is a useful animal for studying genetic crosses. 1. ................................................................................................................................ .................................................................................................................................... 2. ................................................................................................................................ .................................................................................................................................... 3. ................................................................................................................................ .................................................................................................................................... (3) Sir George Monoux Sixth Form College 62 In fruit flies the allele for grey body colour, G, is dominant to the allele for black body, g, and the allele for normal wings, N, is dominant to the allele for vestigial wings, n. A cross between a grey-bodied, normal-winged fly and a black-bodied, vestigial-winged fly resulted in the following offspring. 25 grey-bodied, normal-winged 26 grey-bodied, vestigial-winged 24 black-bodied, normal-winged 27 black-bodied, vestigial-winged (b) (i) Give the genotype of the grey-bodied, normal-winged parent. ........................................................................................................................... (1) (ii) Give the genotypes of the gametes which could be produced by one of the grey-bodied, vestigial-winged offspring. ........................................................................................................................... (1) (c) What ratio would you expect in the offspring produced if the grey-bodied, normal-winged parent had been crossed with a fly of the same genotype? .................................................................................................................................... (1) (Total 6 marks) 37. Read the following passage. Madagascar The island of Madagascar has been described as the laboratory of evolution. It broke away from mainland Africa at least 120 million years ago and, following this, many new species developed. Estimates of the number of plant species on the island vary from 7 370 to 12 000, making it botanically one of the richest areas in the world. Of 400 flowering plant families found worldwide, 200 grow only in Madagascar. Among animals, true lemurs are found nowhere else, and 95 per cent of the country’s 235 known species of reptiles evolved on the island. Over the past 25 years the human population has doubled. Land shortage is leading to clearing of the forest, and Madagascar is now facing deforestation on a massive scale. Scientists have estimated that even if the forest could recover, regeneration could take up to a hundred years. (Reproduced with permission from New Scientist magazine RBI Ltd) (a) Explain what is meant by the term species. .................................................................................................................................... .................................................................................................................................... (2) Sir George Monoux Sixth Form College 63 (b) (i) Explain the processes which might have led to the evolution of new species on the island. ........................................................................................................................... ........................................................................................................................... ........................................................................................................................... ........................................................................................................................... ........................................................................................................................... ........................................................................................................................... ........................................................................................................................... ........................................................................................................................... (4) (ii) Suggest and explain how the number of animal species on the island may have changed as it became ‘botanically one of the richest areas in the world’. ........................................................................................................................... ........................................................................................................................... ........................................................................................................................... ........................................................................................................................... (2) (c) Describe the processes by which forest is able to regenerate after being cleared. .................................................................................................................................... .................................................................................................................................... .................................................................................................................................... .................................................................................................................................... .................................................................................................................................... .................................................................................................................................... .................................................................................................................................... .................................................................................................................................... (4) (Total 12 marks) Sir George Monoux Sixth Form College 64 38. The diagram shows the pathway by which phenylalanine is normally metabolised. phenylalanine enzyme A tyrosine DOPA melanin (dark pigment in skin, hair and eyes) dopamine (brain transmitter involved in motor coordination) Phenylketonuria (PKU) is a condition which results from the absence of enzyme A. People with PKU are homozygous for a recessive allele which fails to produce this enzyme. (a) Use the information shown in the diagram to give one symptom you might expect to be visible in a person who inherits PKU. ..................................................................................................................................... (1) (b) Explain how gene mutation may result in an allele which fails to produce a functional enzyme. ..................................................................................................................................... ..................................................................................................................................... ..................................................................................................................................... ..................................................................................................................................... ..................................................................................................................................... ..................................................................................................................................... (3) Sir George Monoux Sixth Form College 65 (c) (i) A child with PKU was born to two unaffected parents. Complete the genetic diagram to show how this is possible. Parental phenotypes Parental genotypes Genotypes of gametes Genotypes of children Phenotypes of children (2) (ii) What is the probability that a second child born to these parents will have PKU? ........................................................................................................................... (1) (Total 7 marks) 39. Tongue-rolling and red-green colour blindness are two genetically controlled conditions which occur in humans. Tongue-rolling is controlled by the dominant allele, T, while non-rolling is controlled by the recessive allele, t. Red-green colour blindness is controlled by a sex-linked gene on the X chromosome. Normal colour vision is controlled by the dominant allele, B, while red-green colour blindness is controlled by the recessive allele, b. Sir George Monoux Sixth Form College 66 (a) Complete the genetic diagram to show the possible genotypes and phenotypes which could be produced from the following parents. Female Colour blind and heterozygous for tongue-rolling. Male Normal colour vision and non-roller Parental genotypes Genotypes of gametes Genotypes of children Sex and phenotypes of children (4) (b) Explain why a higher percentage of males than females in a population is red-green colour blind. ..................................................................................................................................... ..................................................................................................................................... (c) Sex-linked genes on the Y chromosome have been found in humans and other animal species. Suggest and explain one piece of evidence which would support the presence of such a gene. ..................................................................................................................................... ..................................................................................................................................... (1) (Total 6 marks) Sir George Monoux Sixth Form College 67 40. Fourteen different species of finch live on the isolated Galapagos Islands. The finches are believed to have all evolved from a single common ancestor. The diagram shows the suggested evolutionary relationships amongst the species. Carmahynchus Certhidia olivacea Pinaroloxia inornata heliobates pallidus WARBLER Geospiza pauper parvulus fuliginosa crassirostris magnirostris scandens psittacula conirostris WOODPECKER difficilis fortis FINCHES INSECT EATERS SEED EATERS SEED-EATING GROUND FINCH ANCESTOR (a) Suggest why these fourteen types of finch are considered to be different species. ..................................................................................................................................... ..................................................................................................................................... (1) (b) Use the information in the diagram to identify (i) the species of ground finch which eats the largest seeds; ........................................................................................................................... (ii) the number of genera which are present on the islands. ........................................................................................................................... (2) (c) Suggest how two distinct species, one insect-eating and the other seed-eating, may have evolved from a common ancestor. ..................................................................................................................................... ..................................................................................................................................... ..................................................................................................................................... ..................................................................................................................................... ..................................................................................................................................... (4) (Total 7 marks) Sir George Monoux Sixth Form College 68 Sir George Monoux Sixth Form College 69 41. Some forms of clover are cyanogenic. They produce poisonous hydrogen cyanide when their tissues are damaged. The production of hydrogen cyanide takes place in two steps, each of which is catalysed by an enzyme produced by a different gene. Dominant allele A Dominant allele B Enzyme A Enzyme B Substrate (a) Cyanogenic glucoside Hydrogen cyanide What are the phenotypes (cyanogenic or non-cyanogenic) of the following genotypes? Explain your answer. (i) AABb ........................................................................................................................... ........................................................................................................................... (ii) aaBB ........................................................................................................................... ........................................................................................................................... (3) (b) Two clover plants, each with the genotype AaBb were crossed. (i) Use a genetic diagram to show the genotypes of the offspring. (ii) What is the expected ratio of cyanogenic to non-cyanogenic plants in the offspring? ........................................................................................................................... (3) (c) Cyanogenic clover plants are toxic to slugs. Slugs are common at low altitude but not at high altitude where the climate is colder. When the cells of cyanogenic clover plants freeze, the hydrogen cyanide that is released kills the cells and as a result the plant dies. The frequencies of the alleles for cyanogenesis are different in clover plants growing at low and at high altitudes. (i) How would you expect the allele frequencies to differ? ........................................................................................................................... ........................................................................................................................... Sir George Monoux Sixth Form College 70 Sir George Monoux Sixth Form College 71 (ii) Use the information given to explain how the different allele frequencies might be the result of natural selection. ........................................................................................................................... ........................................................................................................................... ........................................................................................................................... ........................................................................................................................... ........................................................................................................................... ........................................................................................................................... ........................................................................................................................... ........................................................................................................................... ........................................................................................................................... ........................................................................................................................... ........................................................................................................................... ........................................................................................................................... (6) (Total 12 marks) 42. The purple saxifrage is a flowering plant found in the Arctic. It has two distinct forms, one growing on dry ridges, the other in the valleys. On dry ridges, where the temperature is higher and the growing season longer, the plants grow in upright tufts. These plants are drought tolerant and store carbohydrate which they use in times of stress. In the valleys, where it is colder and the growing season is shorter, the plants grow very close to the ground. These plants have a higher rate of photosynthesis and grow more rapidly. Both forms usually complete their life cycle in the short Arctic summer. In unfavourable years, plants in the valleys may produce pollen but are unable to form seeds. Some pollen from the valley plants fertilises plants on the ridges. The seeds may then be washed down to the valleys. Those that develop and complete their life cycles are all low-growing plants. When plants from the ridges and the valleys are grown under identical conditions in the laboratory, they have the same growth form as they did when in their original environment. (Reproduced from The Biologist, R. M. M. Crawford by permission of Institute of Biology) (a) What is the evidence in the passage that the two forms of the purple saxifrage (i) are genetically different; .......................................................................................................................... .......................................................................................................................... (1) Sir George Monoux Sixth Form College 72 Sir George Monoux Sixth Form College 73 (ii) belong to the same species? .......................................................................................................................... .......................................................................................................................... (1) (b) When cross pollination between the low-growing and upright forms occurs, both forms of plant develop when the seeds produced are grown in the laboratory. Explain why only low-growing plants develop from the seeds which are washed from the ridges into the valleys. ..................................................................................................................................... ..................................................................................................................................... ..................................................................................................................................... ..................................................................................................................................... (2) (c) Under the conditions described, the two forms of the purple saxifrage are unlikely to evolve into separate species. Explain why. ..................................................................................................................................... ..................................................................................................................................... ..................................................................................................................................... ..................................................................................................................................... (2) (d) The effect of global warming on the environment of the Arctic is uncertain. Suggest why species such as the purple saxifrage are likely to survive even if changes in climate do occur. ..................................................................................................................................... ..................................................................................................................................... ..................................................................................................................................... ..................................................................................................................................... (2) (Total 8 marks) Sir George Monoux Sixth Form College 74 43. The allele for Rhesus positive, R, is dominant to that for Rhesus negative, r. Haemophilia is a sex-linked condition. The allele for haemophilia, h, is recessive to the allele for normal blood clotting, H, and is carried on the X–chromosome. The diagram shows the Rhesus blood group phenotypes in a family tree where some individuals have haemophilia. male affected with haemophilia unaffected male 1 2 Rhesus positive 3 4 Rhesus positive Rhesus positive 5 6 Rhesus positive Rhesus positive 8 Rhesus negative unaffected female Rhesus negative 7 Rhesus positive 9 10 Rhesus positive Rhesus positive 11 Rhesus positive 12 Rhesus negative (a) (i) Use the information in the diagram to give one piece of evidence that the allele for the Rhesus negative condition is recessive. .......................................................................................................................... .......................................................................................................................... (1) (ii) Explain the evidence from the cross between individuals 3 and 4 that the gene controlling Rhesus blood group is not sex-linked. .......................................................................................................................... .......................................................................................................................... (2) (b) Give the full genotype of (i) individual 6; .......................................................................................................................... (1) (ii) individual 12. .......................................................................................................................... Sir George Monoux Sixth Form College 75 (1) Sir George Monoux Sixth Form College 76 (c) What is the probability that the next child of couple 10 and 11 will have the same genotype as the first child? Show your working. ..................................................................................................................................... ..................................................................................................................................... ..................................................................................................................................... ..................................................................................................................................... ..................................................................................................................................... ..................................................................................................................................... ..................................................................................................................................... ..................................................................................................................................... (3) (Total 8 marks) 44. The maps show the present distribution of malaria and the sickle–cell allele in Africa. Allele frequency 1-10% Areas where malaria occurs Sickle-cell allele Malaria (a) 10-20% Draw a genetic diagram to show how sickle-cell anaemia can be inherited from parents who do not have the condition. Key to symbols for alleles HbA HbS Normal adult haemoglobin Sickle–cell haemoglobin Parental genotypes Gamete genotypes Children’s genotypes Children’s phenotypes (3) Sir George Monoux Sixth Form College 77 (b) In a village with a population of 500, there were 8 people who were homozygous for the sickle–cell allele and 96 who were heterozygous. Calculate the frequency of the HbS allele in the village. Show your working. Answer.............................. (2) (c) One hypothesis to account for the high frequency of the sickle-cell allele in parts of Africa concerns resistance to malaria. (i) Explain the link between sickle cell anaemia, resistance to malaria and the frequency of the HbS allele. ........................................................................................................................... ........................................................................................................................... ........................................................................................................................... ........................................................................................................................... ........................................................................................................................... ........................................................................................................................... ........................................................................................................................... ........................................................................................................................... (3) (ii) Select and evaluate the evidence from the maps which supports this hypothesis. ........................................................................................................................... ........................................................................................................................... ........................................................................................................................... ........................................................................................................................... ........................................................................................................................... (2) Sir George Monoux Sixth Form College 78 (d) Chloroquine is a drug which has been used very successfully to treat malaria. The use of chloroquine to treat malaria has produced changes in the frequency of the HbS allele. Explain how. ..................................................................................................................................... ..................................................................................................................................... ..................................................................................................................................... ..................................................................................................................................... ..................................................................................................................................... (2) (Total 12 marks) 45. The apple maggot fly (Rhagoletis pomonella) was found originally only on hawthorn trees in North America. In the 19th century, it spread as a pest to apple trees introduced into North America by farmers. The flies attacking the apple trees are now genetically different from the flies that attack hawthorn trees. It is thought that a new species of fly may be evolving. (a) Suggest how the flies that feed on apple trees could evolve from those that fed on hawthorn trees. .................................................................................................................................... .................................................................................................................................... .................................................................................................................................... .................................................................................................................................... .................................................................................................................................... .................................................................................................................................... .................................................................................................................................... .................................................................................................................................... (3) Sir George Monoux Sixth Form College 79 (b) Suggest one way in which scientists could find out whether the flies from apple trees were a different species from those found on hawthorn trees. .................................................................................................................................... .................................................................................................................................... .................................................................................................................................... .................................................................................................................................... .................................................................................................................................... .................................................................................................................................... .................................................................................................................................... .................................................................................................................................... (2) (Total 5 marks) 46. (a) Explain what is meant by a recessive allele; .................................................................................................................................... .................................................................................................................................... a sex-linked gene. .................................................................................................................................... .................................................................................................................................... (2) Sir George Monoux Sixth Form College 80 (b) Nail-patella syndrome is an inherited condition caused by a single gene. Sufferers have abnormal nail growth and underdeveloped kneecaps. The pedigree shows how members of one family were affected by the syndrome. Affected male 1 2 Unaffected male Affected female 3 5 6 7 4 8 9 Unaffected female 10 Explain one piece of evidence from the pedigree which indicates that (i) the allele for the nail-patella syndrome is dominant; ............................................................................................................................ ............................................................................................................................ ............................................................................................................................ ............................................................................................................................ (2) (ii) the gene is not sex-linked. ............................................................................................................................ ............................................................................................................................ ............................................................................................................................ ............................................................................................................................ (2) (Total 6 marks) Sir George Monoux Sixth Form College 81 47. The diagram shows the range in wing length of a species of small bird on different islands to the north of Great Britain. 1200 Island 6 900 Distance north of 600 Great Britain/km Island 5 Island 4 Island 3 Island 2 300 Island 1 0 45 (a) (i) 50 55 60 Length of wing/mm 65 70 On which islands might a bird with wings 55mm long live? ............................................................................................................................ (1) (ii) What would be the mid-point of the range of wing length expected on an island that is 750km north of Great Britain? ............................................................................................................................ (1) (b) In this species wing length increases with body size. Suggest how this trend in body size might help the birds to survive. .................................................................................................................................... .................................................................................................................................... .................................................................................................................................... .................................................................................................................................... (2) Sir George Monoux Sixth Form College 82 (c) Explain how selection may have resulted in an increase in body size. .................................................................................................................................... .................................................................................................................................... .................................................................................................................................... .................................................................................................................................... .................................................................................................................................... .................................................................................................................................... (3) (Total 7 marks) 48. Familial polyposis is a hereditary disease. In this disease small wart-like growths appear on the inner surface of the large intestine during childhood. The risk that one of these warts will develop into a malignant tumour in teenage years is so high that affected children are often treated by having that part of the large intestine surgically removed. (a) Suggest one diagnostic technique that could be used to detect familial polyposis in children from a family with a history of this disease. .................................................................................................................................... (1) (b) Explain what is meant by a malignant tumour. .................................................................................................................................... .................................................................................................................................... .................................................................................................................................... .................................................................................................................................... (2) (c) Familial polyposis is caused by a dominant allele, A. The allele is not located on a sex chromosome. In a couple, the male is heterozygous for familial polyposis and the female is unaffected. What is the probability that a child born to this couple would have familial polyposis? Use a genetic diagram to explain your answer. (3) Sir George Monoux Sixth Form College 83 (d) Serious diseases caused by dominant alleles are relatively uncommon compared with diseases caused by recessive alleles. Suggest an explanation for this. .................................................................................................................................... .................................................................................................................................... .................................................................................................................................... .................................................................................................................................... (2) (Total 8 marks) 49. Crigler-Najjar (C-N) syndrome is a rare genetic disorder controlled by a recessive allele. Individuals with the disorder are unable to break down bilirubin, a toxic waste product formed when the liver destroys old red blood cells. Children with this syndrome must sleep under special blue lights which destroy bilirubin. If this treatment fails a liver transplant is required. Although rare in the general population, C-N syndrome is common in one particular community. This community is described as closed as marriage occurs only between its members. (a) Explain what is meant by an allele. .................................................................................................................................... .................................................................................................................................... (1) (b) (i) Use a genetic diagram to show how two people, neither of whom shows the disorder, can have a child with C-N syndrome. (ii) Suggest how C-N syndrome could become common in a closed community. ............................................................................................................................ ............................................................................................................................ ............................................................................................................................ ............................................................................................................................ ............................................................................................................................ ............................................................................................................................ Sir George Monoux Sixth Form College 84 (4) Sir George Monoux Sixth Form College 85 (c) Recent studies have shown that it may be possible to repair the defective gene in the liver cells of affected individuals. Successful gene therapy of all individuals with this disorder in this community might increase the frequency of C-N syndrome in future generations. Suggest how. .................................................................................................................................... .................................................................................................................................... .................................................................................................................................... .................................................................................................................................... (2) (Total 7 marks) 50. In a species of fruitfly, females have two X chromosomes, and males have an X and a Y chromosome. A gene controlling eye shape in fruitflies is sex-linked, and found only on the X chromosome. This gene has two alleles, R for round eyes and B for bar eyes. A homozygous, round-eyed female (XR XR) was crossed with a bar-eyed male. In the offspring (Offspring 1), all the female offspring had wide bar eyes (intermediate in size) and all the males had round eyes. The figure shows the head of three fruitflies Wide bar eye (a) Bar eye Round eye Name the relationship between the two alleles that control eye shape. ..................................................................................................................................... (1) (b) Give the genotype of the male parent. ..................................................................................................................................... (1) Sir George Monoux Sixth Form College 86 (c) Offspring 1 were allowed to interbreed. Complete the genetic diagram to show the phenotypic ratio you would expect in the resulting Offspring 2. Parental phenotypes Parental genotypes Offspring 1 phenotypes Round-eyed female Bar-eyed male XR XR Wide bar-eyed female Round-eyed male Offspring 1 genotypes Gametes Offspring 2 genotypes Offspring 2 phenotypes and ratio (3) (Total 5 marks) 51. Thalassemia is a disease in which people homozygous for the recessive allele, t, show a severe anaemia. Before suitable medical treatment was available, they did not usually survive childhood. Heterozygotes are only mildly affected, but are more resistant to malaria than people who are homozygous dominant, TT. The graph shows the relationship between altitude and the frequency of the thalassemia allele, t, for a group of villages on the Italian island of Sardinia. The information relates to the early 20th century. Sir George Monoux Sixth Form College 87 The frequency of the allele t in a population can be calculated from the formula 1 number of Tt genotypes) 2 total number of people (Number of tt genotypes 0.24 0.20 0.16 Frequency of t allele 0.12 0.08 0.04 Carloforte 0 sea level (a) 200 400 600 800 1000 Altitude / m Ignoring the information for the village of Carloforte, describe the relationship between the frequency of the t allele and altitude. ..................................................................................................................................... ..................................................................................................................................... ..................................................................................................................................... (2) Until the late 19th century, malaria was commonly found among people living at low altitudes in Sardinia. It is a serious blood disease caused by a parasite which is carried in the salivary glands of certain species of mosquito. These mosquitoes, which thrive in warm conditions near to sources of still or slow-moving water, infect humans with malaria by biting them. (b) Suggest an explanation for the higher frequency of the t allele found at certain altitudes. ..................................................................................................................................... ..................................................................................................................................... ..................................................................................................................................... ..................................................................................................................................... ..................................................................................................................................... ..................................................................................................................................... ..................................................................................................................................... (3) Sir George Monoux Sixth Form College 88 (c) Information for the village of Carloforte is shown on the graph as a square. This village was founded more recently, by families from mainland Italy. Suggest two possible reasons for the unusually low frequency of the t allele found at Carloforte. 1. ................................................................................................................................. ..................................................................................................................................... ..................................................................................................................................... 2. ................................................................................................................................. ..................................................................................................................................... ..................................................................................................................................... (2) (Total 7 marks) 52. A species of flowering plant can have white, red or purple flowers. The colour of the flowers is controlled by two genes. Each gene is found on a different chromosome, and is responsible for one step in a biosynthetic pathway. The biosynthetic pathway is gene 1 gene 2 enzyme 1 enzyme 2 J K L colourless substance red pigment purple pigment Gene 1 has the dominant allele A and the recessive allele a. Gene 2 has the dominant allele B and the recessive allele b. In both cases, the dominant allele needs to be present for the production of the associated enzyme. Sir George Monoux Sixth Form College 89 (a) Explain how the two genes are involved in producing white, red or purple flowers. ..................................................................................................................................... ..................................................................................................................................... ..................................................................................................................................... ..................................................................................................................................... ..................................................................................................................................... ..................................................................................................................................... ..................................................................................................................................... ..................................................................................................................................... ..................................................................................................................................... ..................................................................................................................................... ..................................................................................................................................... ..................................................................................................................................... ..................................................................................................................................... (6) (b) (i) A homozygous red-flowered plant was crossed with a homozygous white-flowered plant. All the flowers of the offspring were purple. What was the genotype of the red-flowered parent; ........................................................................................................................... the white-flowered parent? ........................................................................................................................... (2) Sir George Monoux Sixth Form College 90 (ii) The purple-flowered offspring were crossed. What phenotypic ratio would you expect in the next generation? Use a genetic diagram to explain your answer. (4) (c) (i) Genetically, there are different types of white-flowered plants of this species. Give their different genotypes. ........................................................................................................................... (1) (ii) You have samples of fresh petals from the two homozygous types of white flowers, and a pure sample of the red pigment, K. Explain, in outline, how you might distinguish the two types of petal from each other. ........................................................................................................................... ........................................................................................................................... ........................................................................................................................... ........................................................................................................................... ........................................................................................................................... (2) (Total 15 marks) Sir George Monoux Sixth Form College 91 53. The diagram shows the inheritance of coat colour in pigs through three generations. 1 2 5 3 6 7 12 4 8 9 10 13 14 15 Key: Square = male Circle = female 11 16 17 18 red sandy white (a) Explain one piece of evidence from the diagram which shows that coat colour is not controlled by one gene with two codominant alleles. .................................................................................................................................... .................................................................................................................................... .................................................................................................................................... .................................................................................................................................... .................................................................................................................................... .................................................................................................................................... .................................................................................................................................... (3) Two hypotheses were put forward to explain the results, each based on the action of two pairs of alleles. Hypothesis 1 Hypothesis 2 Phenotype Genotype Genotype Red A_B_ A_B_ or A_bb Sandy A_bb or aaB_ aaB_ White aabb aabb ( _ represents either a dominant or a recessive allele of the gene) Sir George Monoux Sixth Form College 92 (b) Assuming that Hypothesis 1 is correct, give one possible genotype for each of the following individuals in the diagram. 11 ..................................................... 10 ..................................................... 2 ....................................................... (2) (c) Explain one piece of evidence from the diagram which shows that Hypothesis 2 should be rejected. .................................................................................................................................... .................................................................................................................................... .................................................................................................................................... .................................................................................................................................... (2) Sir George Monoux Sixth Form College 93 (d) Individual 18 was crossed with a pig of genotype Aabb. Use Hypothesis 1 to predict the genotypes and the ratio of phenotypes expected in the offspring of this cross. Individual 18 Parental genotypes ................................. Other parent Aabb Parental gametes Offspring genotypes Offspring phenotypes Expected ratio of offspring phenotypes (4) (Total 11 marks) Sir George Monoux Sixth Form College 94 54. The diagram shows the chromosomes from a plant cell in which 2n = 4. The plant is heterozygous for two characteristics: height (the alleles T = tall and t = dwarf); flower colour (the alleles B = blue and b = white); Allele T is dominant to allele t and allele B is dominant to allele b. Chromatid T Centromere (a) (i) T t t b b B B In the space below, draw a diagram to show the appearance of these chromosomes just as they are beginning to separate in the first stage of meiosis. (2) (ii) Give all the different genotypes of the gametes produced at the end of meiosis in this plant. .......................................................................................................................... (1) Sir George Monoux Sixth Form College 95 The plant is also heterozygous for another characteristic, the colour of its stem. The alleles responsible (A = purple stem, a = green stem) are carried on the same pair of chromosomes as the alleles for height. Allele A is dominant to allele a. The pair of chromosomes is shown in the diagram. T A T A t t a a The plant was crossed with a dwarf, green-stemmed plant and produced a large number of offspring. The table shows the results. (b) Phenotype Tall, purplestemmed Tall, greenstemmed Dwarf, purplestemmed Dwarf, green-stemme d Number of offspring 91 9 11 89 (i) Explain how crossing over accounts for the fact that the offspring include some individuals which are tall and green-stemmed and some which are dwarf and purple-stemmed. .......................................................................................................................... .......................................................................................................................... .......................................................................................................................... .......................................................................................................................... .......................................................................................................................... (2) (ii) Suggest why there are fewer offspring with these phenotypes. .......................................................................................................................... .......................................................................................................................... (1) Sir George Monoux Sixth Form College 96 (iii) When observing dividing cells under a microscope, how would you recognise that crossing over had taken place? .......................................................................................................................... .......................................................................................................................... (1) (c) Give two factors, other than crossing over, which result in genetic variation in the offspring produced by a sexually reproducing organism. In each case, explain how the factor brings about genetic variation. .................................................................................................................................... .................................................................................................................................... .................................................................................................................................... .................................................................................................................................... .................................................................................................................................... .................................................................................................................................... .................................................................................................................................... .................................................................................................................................... (4) (Total 11 marks) 55. The male peacock has very long, brightly coloured tail feathers decorated with ‘eye spots’. The drawing shows a male peacock displaying to a female. Sir George Monoux Sixth Form College 97 S There is variation in the number of eye spots on the tails of male peacocks. A positive correlation exists between the number of eye spots and the number of females that a male mates with. Suggest how natural selection may have produced an increase in the number of eye spots over time. ............................................................................................................................................... ............................................................................................................................................... ............................................................................................................................................... ............................................................................................................................................... ............................................................................................................................................... ............................................................................................................................................... ............................................................................................................................................... (Total 3 marks) 56. (a) Explain what is meant by (i) a recessive allele; .......................................................................................................................... .......................................................................................................................... (ii) codominant alleles. .......................................................................................................................... .......................................................................................................................... (2) (b) Chickens homozygous for black feathers were crossed with chickens homozygous for white feathers. These colours are determined by alleles of a single gene. All the F1 offspring had blue feathers. When the blue-feathered F1 chickens were crossed with each other, there were black-feathered, white-feathered and blue-feathered chickens in the F2 offspring. (i) Complete the genetic diagram to explain. how the F1, and F2 phenotypes were produced. Parental phenotypes Parental genotypes Sir George Monoux Sixth Form College Black-feathered FBFB White-feathered FWFW 98 F1 genotype F1, gametes F2 genotypes F2 phenotypes Black-feathered White-feathered Blue-feathered (4) (ii) The number of black-feathered, white-feathered and blue-feathered chickens in the F2 offspring was counted. The observed ratio of black : white : blue was similar to the ratio expected from theory but not the same. Explain why observed ratios are often not the same as the expected ratios. .......................................................................................................................... .......................................................................................................................... .......................................................................................................................... .......................................................................................................................... (2) (Total 8 marks) 57. (a) Explain how natural selection produces changes within a species. ..................................................................................................................................... ..................................................................................................................................... ..................................................................................................................................... ..................................................................................................................................... ..................................................................................................................................... ..................................................................................................................................... ..................................................................................................................................... ..................................................................................................................................... ..................................................................................................................................... ..................................................................................................................................... (4) Sir George Monoux Sixth Form College 99 (b) Malaria is caused by a parasite that attacks red blood cells, producing repeated bouts of serious illness and often causing death. The allete for normal haemoglobin in red cells is HbA. In the West African country of Burkina Faso, twenty percent of people are heterozygous for a different allele, HbC, which has no effect on their health. People homozygous for HbC suffer a very mild anaemia. The bar chart shows how the HbC allele affects the chance of getting malaria. 80 70 Percentage of 60 people with malaria compared 50 to HbAHb A 40 genotype 30 20 10 0 HbA Hb C HbC Hb C Genotype (i) Use the bar chart to describe how the HbC allele affects the chance of getting malaria. .......................................................................................................................... .......................................................................................................................... .......................................................................................................................... .......................................................................................................................... (2) (ii) Malaria is very common in Burkina Faso. The HbC allele is increasing in frequency in this part of Africa. Suggest an explanation for this. .......................................................................................................................... .......................................................................................................................... .......................................................................................................................... .......................................................................................................................... (2) (Total 8 marks) Sir George Monoux Sixth Form College 100 58. Small clearings in woods may occur when large trees die or are blown down. This allows herbaceous plants to grow for a few years. One plant species that commonly colonises woodland clearings is the foxglove. (a) Name and describe the ecological process which will result in the disappearance of foxgloves from a clearing after a few years. ..................................................................................................................................... ..................................................................................................................................... ..................................................................................................................................... ..................................................................................................................................... ..................................................................................................................................... ..................................................................................................................................... (3) S (b) The foxglove is a biennial plant, which means that it lives for two years. In the first year it produces leaves but no flowers. In the second year it flowers and each plant releases about 300 000 very small seeds. (i) Suggest how being a biennial enables a foxglove plant to produce very large numbers of seeds. .......................................................................................................................... .......................................................................................................................... .......................................................................................................................... .......................................................................................................................... (2) (ii) Suggest how producing large numbers of very small seeds adapts the foxglove for colonising woodland clearings. .......................................................................................................................... .......................................................................................................................... .......................................................................................................................... .......................................................................................................................... (2) Sir George Monoux Sixth Form College 101 S (c) The leaves of foxgloves contain a poisonous substance, called digitalis. In high concentrations, digitalis slows down the rate at which impulses pass across the atria of the heart. Explain how the presence of digitalis may protect foxgloves from being eaten by mammals. ..................................................................................................................................... ..................................................................................................................................... ..................................................................................................................................... ..................................................................................................................................... ..................................................................................................................................... ..................................................................................................................................... (3) (Total 10 marks) 59. (a) Explain what is meant by (i) an allele; .......................................................................................................................... .......................................................................................................................... (ii) a sex-linked gene. .......................................................................................................................... .......................................................................................................................... (2) (b) Becker muscular dystrophy is an inherited condition caused by an allele of a gene. Sufferers experience some loss of muscle strength. The diagram shows how members of one family were affected by the condition. 1 Affected male 2 Unaffected male 3 6 7 Sir George Monoux Sixth Form College 4 8 9 Unaffected female 5 10 11 102 (i) Explain one piece of evidence from the diagram which shows that the allele for Becker muscular dystrophy is recessive. .......................................................................................................................... .......................................................................................................................... .......................................................................................................................... .......................................................................................................................... (2) (ii) The allele for Becker muscular dystrophy is sex-linked. Explain how individual 9 inherited the condition from his grandfather. .......................................................................................................................... .......................................................................................................................... .......................................................................................................................... .......................................................................................................................... (2) (Total 6 marks) 60. Seeds were obtained from a species of grass growing in a field (Group F) and from the same species growing on the waste tip of an old copper mine (Group M). Both seed samples were grown in soil containing high concentrations of copper. After a set time, the height of the grass plants was measured to the nearest millimetre. The results are shown in the histograms. 50 Plants grown from seeds from field grass (Group F) Number 40 of 30 plants 20 10 0 10 20 30 40 50 60 70 80 90 100 110 120 130 140 150 Plant height / mm 15 Plants grown from seeds from mine-waste grass (Group M) Number 10 of plants 5 0 10 20 30 40 50 60 70 80 90 100 110 120 130 140 150 Plant height / mm Sir George Monoux Sixth Form College 103 (a) Describe the growth of Group F and Group M plants when grown in soil containing high concentrations of copper. ..................................................................................................................................... ..................................................................................................................................... ..................................................................................................................................... ..................................................................................................................................... (2) (b) Suggest an explanation for the difference in growth between Group F and Group M plants. ..................................................................................................................................... ..................................................................................................................................... ..................................................................................................................................... ..................................................................................................................................... (2) (c) Suggest an explanation to account for the one Group F plant that grew to 110-119 mm. ..................................................................................................................................... ..................................................................................................................................... ..................................................................................................................................... ..................................................................................................................................... (2) (Total 6 marks) Sir George Monoux Sixth Form College 104 61. Answers should be written in continuous prose, where appropriate. Quality of Written Communication will be assessed in these answers. In California there are different types of Ensatina eschscholtzi, each with a characteristic appearance and found in its own area. They are sufficiently different from each other to be classified as subspecies. These may become new species with time. The map shows the distribution of populations of four subspecies. Ensatina eschscholtzi oregonensis Mountain ranges E.eschscholtzi platensis E.eschscholtzi xanthoptica X (i) Suggest how speciation may be occurring in these salamanders. ..................................................................................................................................... ..................................................................................................................................... ..................................................................................................................................... ..................................................................................................................................... ..................................................................................................................................... ..................................................................................................................................... ..................................................................................................................................... ..................................................................................................................................... (4) Sir George Monoux Sixth Form College 105 (ii) Suggest one way in which scientists could find out whether the salamanders from the area marked X were a different species from those found in other areas. ..................................................................................................................................... ..................................................................................................................................... ..................................................................................................................................... ..................................................................................................................................... (2) (iii) Within each subspecies there is a range of phenotypes. Explain the factors that give rise to this variation. ..................................................................................................................................... ..................................................................................................................................... ..................................................................................................................................... ..................................................................................................................................... ..................................................................................................................................... ..................................................................................................................................... ..................................................................................................................................... ..................................................................................................................................... (4) (Total 10 marks) 62. A sex-linked gene controls fur colour in cats. Ginger-coloured fur is controlled by the allele G, and black-coloured fur is controlled by the allele g. Some female cats have ginger and black patches of fur. They are described as tortoiseshell. Male cats cannot be tortoiseshell. (a) What is meant by a sex-linked gene? ..................................................................................................................................... ..................................................................................................................................... (1) (b) A male cat with the genotype Xg Y mates with a tortoiseshell female. (i) Give the phenotype of the male. ........................................................................................................................... (1) (ii) Give the genotype of the tortoiseshell female. ........................................................................................................................... (1) Sir George Monoux Sixth Form College 106 (iii) Complete the genetic diagram to show the genotypes and the ratio of phenotypes expected in the offspring of this cross. Parents Male Parental genotypes Xg Y Tortoiseshell female ……………… Parental gametes Offspring genotypes Offspring phenotypes Ratio (3) Sir George Monoux Sixth Form College 107 (c) The effect of the G and g alleles is modified by another gene. This gene is not sex-linked and it has two alleles. The allele d changes the ginger colour to cream and the black colour to grey. The dominant allele D does not modify the effect of G or g. A cream-coloured male cat mated with a black female whose genotype was XgXg Dd. Male kittens of two different colours were produced. Complete the genetic diagram. Parental phenotypes Cream-coloured male Black female Parental genotypes ……………… XgXg Dd Parental gametes Male kitten genotypes Male kitten colours (3) (Total 9 marks) 63. In an attempt to control the huge numbers of an insect pest, low doses of a pesticide were sprayed on a lake. After spraying, the concentration of pesticide in the lake water was 14 parts per billion. After spraying, diving birds which fed on small fish in the lake were found to be dying. The concentration of the pesticide in these birds was more than 1 part per thousand. (a) Explain why the pesticide was in such a high concentration in the diving birds. ..................................................................................................................................... ..................................................................................................................................... ..................................................................................................................................... ..................................................................................................................................... ..................................................................................................................................... ..................................................................................................................................... (3) Sir George Monoux Sixth Form College 108 S (b) The lake was sprayed three times. The first spraying killed almost all of the insects, as did a second application five years later. When the lake was treated for a third time it was found that some insects were resistant to the pesticide. Explain how resistance to the pesticide evolved in the insect population. ..................................................................................................................................... ..................................................................................................................................... ..................................................................................................................................... ..................................................................................................................................... ..................................................................................................................................... ..................................................................................................................................... (3) S (c) This pesticide is able to pass easily through cell membranes. Suggest why. ..................................................................................................................................... ..................................................................................................................................... ..................................................................................................................................... ..................................................................................................................................... (2) (Total 8 marks) Sir George Monoux Sixth Form College 109 64. (a) A protein found on red blood cells, called antigen G, is coded for by a dominant allele of a gene found on the X chromosome. There is no corresponding gene on the Y chromosome. The members of one family were tested for the presence of antigen G in the blood. The antigen was found in the daughter, her father and her father’s mother, as shown in the genetic diagram below. No other members had the antigen. Grandmother (has antigen G) Genotypes ……… or ……… Gamete genotypes ……… or ……… Grandfather Grandmother ………… ………… ………… ………… ………… ………… Father (has antigen G) Genotypes Grandfather Mother ……… ……… Gamete ……… ……… genotypes Daughter (has antigen G) Genotype ……… (i) One of the grandmothers has two possible genotypes. Write these on the genetic diagram, using the symbol XG to show the presence of the allele for antigen G on the X chromosome, and Xg for its absence. (1) (ii) Complete the rest of the diagram. (3) (iii) The mother and father have a son. What is the probability of this son inheriting antigen G? Explain your answer. Probability ..................................................... ......................................................................................................................…. ......................................................................................................................…. (2) Sir George Monoux Sixth Form College 110 (b) During meiosis, when the X and Y chromosomes pair up, they do not form a typical bivalent as do other chromosomes. Explain why. ................................................................................................................................…. .................................................................................................................................... ..................................................................................................................................... ..................................................................................................................................... (2) (Total 8 marks) Sir George Monoux Sixth Form College 111
