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Name: Evolutionary Processes Workbook 3 Year 13 Science 2016 Populations and Gene Flow A population is the members of a species that live in the same geographical location and have a common gene pool. Gene flow occurs when individuals move from one population to another. A deme is a local population that has limited gene flow with members of the larger population. 1. Which demes make up population 1? A and B 2. Which demes make up population 2? C, D, E, F, G and H Example: Moths in a deme in one part of an area of bush may all be slightly lighter in colour than moths in a neighbouring deme where the bush is denser and is darker. A cline is a pattern of variation between individuals where there is continuous increase or decrease in some phenotypic characteristic between populations that are adjacent. Sometimes individuals at one end of a cline are so different than those at the other end that they cannot interbreed – they are separate species. Example: Populations of tomtits in New Zealand have longer wings and tails the further south they are found. A ring species occurs when a cline has formed a circle (often around the globe) and where the ends of the cline meet the organisms are so different that two separate species are seen. There is a range of intermediate forms between the two species. Example: There is a continuous ring of populations of warblers around the Tibetan Plateau. The birds’ behaviour and genetic characteristics change gradually around the ring, which is broken in Siberia where two forms of the warbler live but do not interbreed, because their mating calls are so different. 3. Which diagram represents a cline? A 4. Which diagram represents a ring species? B 5. Why are Species A and Species E unable to interbreed? One species is so different from the other that they are unable to interbreed 6. Write a definition for each of the key words in the table - in your own words definition members of a species that live in the same geographical location and have a common gene pool. b gene flow individuals move from one population to another – carry their genes with them c deme a local population that has limited gene flow with members of the larger population d cline a pattern of variation between individuals where there is continuous increase or decrease in some phenotypic characteristic between populations that are adjacent e ring species occurs when a cline has formed a circle (often around the globe) and where the ends of the cline meet the organisms are so different that two separate species are seen Genetic drift is the random change in allele frequencies in a population. Genetic drift is determined by chance not by natural selection. Genetic drift is significant in small population as there is a higher probability of alleles being lost (or fixed) by chance than in large population. a 7. Keyword population Why is the diagram above an example of genetic drift? the example shows a small population where allelles have been lost randomly The founder effect occurs when a small population (the founder population) becomes isolated from the main (original) population, often on an island. The alleles that are present and their frequency may not be representative of the original population and the founder population is much more subject to genetic drift. The limited gene pool, inbreeding and genetic drift all mean that there is limited genetic variation in the population. 8. What is the founder population called in the diagram demonstrating the founder effect? colonisers 9. What is the main /original population called in the diagram? Ancestral A bottleneck effect occurs when a large population is suddenly reduced in size, the result of a catastrophic environmental event (e.g. fire, flood, landslip, severe weather) or human impact (habitat destruction, introduction of predator or competitor). The bottleneck may randomly alter allele frequencies and/or remove alleles so that when the population recovers, alleles frequencies may not be representative of the original population and genetic diversity is likely to be reduced. When small (in its ‘bottleneck’ phase), the population is subject to genetic drift (as well as inbreeding) which may further reduce genetic diversity. Lack of diversity in small population increases the likelihood of their extinction should there be a change in the environment. 8. Is the parent population genetically diverse? yes 9. What are three examples of bottlenecking events? Fire, flood, landslip, severe weather, habitat destruction, predator introduction, competitor introduction 10. Is the post-bottleneck population genetically diverse? No 11. Write a definition for each of the key words in the table – in your own words a Keyword genetic drift definition random change in allele frequencies in a population b founder effect c Bottleneck effect when a small population becomes isolated from the main (original) population, often on an island when a large population is suddenly reduced in size 12. Give the main difference in the way that natural selection and genetic drift affect allele frequencies in a gene pool. Natural selection increases the frequency of alleles in the gene pool that produce phenotypes which are successful (fitter) Genetic drift increases frequency of alleles in the gene pool by chance and does not relate to fitness 13. Explain why a founder population is more subject to genetic effect than the parent population. founder populations are small and their gene pool is unlikely to be representative of the parent population – certain alleles may be much reduced in frequency the effect of chance is likely to have a greater effect on allele frequencies than in the larger, parental populations – some alleles may be lost 14. Find and describe two different named examples of the bottleneck effect resulting from human impact in New Zealand. introduction of predators / habitat loss has greatly reduced populations of many native birds e.g. saddleback, stitchbird – numbers have been greatly reduced, conservation measures have been restoring populations black robin – Chatham islands 15. Name the effect, pattern, or population group for each of the following situations. a. Hunting of northern elephant seals reduced the seal’s population to just 20 individuals at the end of the 19th century. Although there are now more than 30 000 animals, they have much less genetic variation than the population of southern elephant seals that was not hunted so intensely. population bottleneck b. The Afrikaner population in South Africa is descended mainly from just a few thousand Dutch colonists. Today, their population has an unusually high frequency of the Huntington’s disease gene. founder effect c. Feathers on the abdomen of birds called ‘Redstarts’ show a change from deep red to orange and then to bright yellow, in a line from Mexico south to the Andes. cline d. A number of different tribal groups live in areas of the New Guinea Highlands, separated by deep ravines and rives. They hardly ever meet. demes 16. Retinitis pigmentosa is an inherited condition that leads to blindness. It results from a recessive allele. Tristan da Cunha is a small island in the Atlantic Ocean. In 1814, 15 people founded a British colony on the island, one of them was a carrier for retinitis pigmentosa. After 150 years, 240 descendants of the original settlers were living on the island, amongst whom four suffered from this form of inherited blindness while nine other were carriers. a. How did the allele for retinitis pigmentosa arise? allele likely the result of gene mutation b. Explain what is meant by a carrier for the condition. has dominant normal allele and recessive mutant allele have normal phenotype – can pass on mutant allele to offspring c. Explain the high incidence of the condition amongst the descendants of the settlers of the island. small original population was a founder population – the occurrence of the mutant allele in the original population of 15 was not representative of the frequency of the allele in the large British population – much higher in the founder population inbreeding increased the frequency of the mutant allele in the population and increased the chances of two mutant alleles coming together to produce a phenotype with retinitis pigmentosa hence the high occurrence of the condition and carriers of the condition in the population of descendants 17. Which type of evolution occurs at the level of the species or above? macroevolution 18. Which type of evolution has small changes in gene frequencies? microevolution 19. Which type of evolution cannot be directly observed? macroevolution 20. What type of evidence would be used to support macroevolution? fossils 21. Which type of evolution could be observed over a few generations? microevolution 22. Which type of evolution could be observed from experimental evidence? microevolution Isolating Mechanisms Speciation (macroevolution) occurs when populations become reproductively isolated – gene flow no longer occurs. Sympatric species are closely related species that live in the same geographic location. Allopatric species are closely related species that live in different geographic locations. An isolating mechanism is any factor that stops two species from interbreeding – a barrier to gene flow. Prezygotic (before the fertilised egg) mechanism act before fertilisation of an egg. Postzygotic mechanisms act after fertilisation. Sometimes, reproductive isolation comes from a mix of several prezygotic and postzygotic factors. 23. a b Write a definition for each of the key words in the table – in your own words Keyword speciation definition when populations become reproductively isolated – gene flow no longer occurs. closely related species that live in the same geographic location e sympatric species allopatric species isolating mechanism prezygotic f postzygotic after fertilisation g reproductive isolation something that stops species from reproducing c d closely related species that live in different geographic locations any factor that stops two species from interbreeding – a barrier to gene flow before fertilisation of an egg Pre-mating Barriers – before mating Geographical isolation - physical barrier separates populations Habitat (ecological) isolation - populations occur in different habitats but in the same area Temporal (seasonal) isolation - mating or flowering occurs at different time or different seasons Behavioural isolation - courtship and mating behaviours are different Structural (anatomical) isolation - physical non-correspondence of reproductive parts Post-mating barriers - after mating Gamete incompatibility 24. - sperm cannot fertilise eggs of a different species Match up the type of prezygotic isolation with the example in the table below. geographical habitat temporal a. Type of prezygotic isolation habitat b. structural c. behavioural d. temporal e. structural f. geographical g. gamete behavioural structural gamete structural Example of prezygotic isolation Herbivorous insects from two populations feed and mate on different host plants Different species of flowering plants are adapted for pollination by particular types of animal only Cricket songs differ in frequency between species, so each cricket attracts a mate only from its own species Dacrydium colensoi (silver pine) sheds pollen in October Dacrydium cupressinium (rimu) sheds pollen in mid-November Mating takes place in insects but males cannot transfer sperm to females because sex organs do not fit together When melting ice and subsequent rise in sea level separated New Zealand into the North and South Islands, two genetically isolated populations of birds were produced form one ancestral population leading to the speciation of kaka in the north and kea in the south. Male gametes are transferred, but sperm do not penetrate the egg surface, e.g. eggs of kina are not fertilised in the water by sperm from other echinoderm species. Postzygotic Mechanisms Hybrid inviability - some species that do not normally interbreed occasionally do so the young die at some point early in their development Hybrid sterility - the offspring reach maturity but are infertile Hybrid breakdown - backcross (F2 – second generation) hybrids have reduced fertility 25. Match up the type of postzygotic isolation with the example in the table below. Hybrid inviability a. Type of postzygotic isolation Hybrid sterility b. Hybrid breakdown c. Hybrid inviability Hybrid sterility Hybrid breakdown Example of postzygotic isolation Mule is a hybrid between a male donkey (2N = 62) and a female horse (2N = 64). The mule has 63 chromosomes and is infertile. Cotton species – F1 (first generation) hybrids are fully fertile, but F2 (second generation) are not. Hybrids between the frogs Rana pipiens and Rana sylvatica do not survive in the tadpole stage for longer than a day. 26. Describe the difference between a prezygotic and postzygotic isolating mechanism. Prezygotic mechanisms act before fertilisation and postzygotic mechanisms act after fertilisation 27. For each of the following, state the isolating mechanism that is described. c. Type of isolation mechanism Gamete incompatibility Geographical isolation Temporal isolation d. Structural isolation e. Hybrid inviability f. Structural isolation g. Behavioural isolation a. b. Example of isolating mechanism Sperm from male duck cannot fertilise the eggs of a turkey A population of a rare snail species is separated into two when a motorway was built Two frog species live in the same pond, but they breed at different times of the year Male fruit flies from one species cannot mate with the females from another species because their sex organs are not compatible Hybrid tadpoles from frogs of two species of the genus Rana die before becoming mature adults Two different species of Columbine have different flower structures and are pollinated by different animals The mating call of a male thrush is not recognised as a mating call by a female blackbird 28. Giant petrels are found throughout the Southern Ocean. There are two closely related species of giant petrel, Macronectes halli and M. giganteus. They breed sympatrically on a number of sub-Antarctic islands. The two species are very similar in appearance and behaviour, with no obvious differences in courtship and mating behaviour. M halli females begin laying eggs about six weeks before M giganteus females. Some interspecific pairs successfully mate and produce young. Explain the isolating mechanism between the two species and how it might have evolved. the isolating mechanism is temporal – the two species have breeding seasons 6 weeks apart which means that pairs of one species will have courted, mated, and be raising their young before the other species arrives to begin their courtship and mating this greatly reduces the chances of adults of the two species coming together and accidently mating the different timing in reproductive behaviour reduces interspecific competition, especially for food, which assists the chances of successful raising of healthy offspring and so the survival of the population / species se 29. A selection of damselfly penises shows the complicated structure of insect sex organs What type of isolating mechanism is this? 30. structural isolating mechanism What type of isolating mechanism is shown in the graph? Temporal isolating mechanism