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1. Figure 2 shows the cycle of a somatic cell. S G1 C Daughter cells G2 Nuclear division Figure 2 a) Define cell cycle. __________________________________________________________________ [1 mark] b) (i) What is the longest phase in interphase? _______________________________________________________________ [1 mark] (ii) State the events that occur in b) (i). _______________________________________________________________ _______________________________________________________________ _______________________________________________________________ [3 marks] c) What happens during S phase? Give two significance of the phase. __________________________________________________________________ __________________________________________________________________ __________________________________________________________________ [3 marks] d) (i) Name the process labelled C. _______________________________________________________________ [1 mark] (ii) In animal cell, C involves the formation of cleavage furrow but not in plant cell. Explain why? _______________________________________________________________ [1 mark] 2. a) In human, cystic fibrosis is caused by a recessive allele, f, of a particular gene. The albino condition, in which no melanin is produced in the skin, is determined by a recessive allele, a, of another skin. These two genes are found on a different chromosome. (i) What is meant by allele? ____________________________________________________________ [1 mark] (ii) An unaffected individual, who is heterozygous from both albinism and cystic fibrosis can produce a range of gametes with respect to these two genes. With reference to meiosis, describe how the difference in the gametes can arise. ____________________________________________________________ ____________________________________________________________ ____________________________________________________________ ____________________________________________________________ [2 marks] (iii) Two individuals, heterozygous for albinism produce a child. Calculate the probability that this child is albino. [2 marks] b) In cats, long hair is controlled by a dominant allele, L, while short hair is controlled by its recessive allele, l. On the other hand, brown hair is controlled by a dominant allele, B, while white hair is controlled by its recessive allele, b. Based on the information given, answer the following questions: (i) Determine the expected phenotypic ratio among F1 progeny for the cross between heterozygous cats. [2 marks] (ii) What percentage of the F1 progenies in cross (i) is expected to be pure breed? ________________________________________________________ [1 mark] (iii) What percentage of F1 progenies in cross (i) can be used as a test cross parent? _________________________________________________________ [1 mark] (iv) What percentage of F1 progenies in cross (i) is expected to have short and brown hair? _________________________________________________________ [1 mark] 3. Phenylketonuria (PKU) is a genetic diseases controlled by the recessive allele. It is also an inborn error of phenylalanine metabolism and leads to severe mental retardation. Table 1 shows the number of the normal and the abnormal individuals in a population. YEAR The number of the normal individuals The number of the abnormal individuals (having (PKU) Total 1995 4996 4 5000 2005 4992 8 5000 Table 1 a) (i) Calculate the frequency of the recessive allele in 1995 and 2005. [2 marks] (ii) Give the conclusion of the allele frequency at a (i). ____________________________________________________________ [1 mark] (iii) Give three assumptions to calculate the allele frequency. ____________________________________________________________ ____________________________________________________________ ____________________________________________________________ [3 marks] 4. a) (i) State the Hardy-Weinberg principle. ____________________________________________________________ ____________________________________________________________ [2 marks] (ii) One of the condition for this principle to be achieved is large population size. Explain why? ____________________________________________________________ ____________________________________________________________ _____________________________________________________________ [3 marks] b) In a randomly breeding population of mice, black coat (H) is dominant to white coat (h). In the population, 36% have white coats. Calculate the genotype frequencies of black coat mice in this population. [2 c) marks] In a human population, the frequency of the recessive individuals for extra-long eyelashes is 90 per 1000. What is the individual percentage of this population that carries recessive allele but displays the phenotype of short eyelashes? [3 marks]