17. Selection and evolution
A section of Biology, 9700
Listing 10 of 104 questions
The fruitfly, Drosophila, has many different species. Three of these species, Drosophila pseudoobscura, D. persimilis and D. miranda, are thought to be closely related. Samples of these three species were collected from the western United States of America. shows where these species naturally occur. Key D. pseudoobscura D. persimilis and D. miranda The base sequences of four regions of DNA of each species were sequenced. The divergence of these base sequences in D. pseudoobscura and D. persimilis from the sequences in D. miranda was calculated. The results are shown in Table 5.1. Table 5.1 DNA region Drosophila species percentage divergence of base sequence from that of D. miranda pseudoobscura 2.5 persimilis 2.4 pseudoobscura 8.1 persimilis 7.3 pseudoobscura 2.1 persimilis 1.7 pseudoobscura 1.9 persimilis 1.7 With reference to Table 5.1, describe the evidence that D. miranda may be more closely related to D. persimilis than to D. pseudoobscura. Suggest why there is more divergence in some regions of DNA than in others. The area where D. pseudoobscura is found is separated from the areas where the other two species are found by a high range of mountains. Explain how the species D. pseudoobscura could have evolved from a population of D. miranda.
9700_s10_qp_43
THEORY
2010
Paper 4, Variant 3
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The puma, Puma concolor, lives in North and South America. shows a puma. Fig 5.2 shows the distribution of the puma species. puma distribution Florida Texas A B Members of different subspecies belong to the same species but have some morphological differences and are found in different geographical locations. In the past the puma has been divided into 32 subspecies. The subspecies of puma varied in body size, coat colour and behaviour to adapt each population to its environment. Explain how the different subspecies of puma evolved. In 2016, genetic analysis concluded that there are only two genetically distinct subspecies of puma, one in North and Central America and one in South America. Outline how practical techniques could be used to conduct a genetic analysis of the puma species. shows the location of an isolated puma population in Florida. In 1990, the size of this population was very small, with fewer than 30 individuals. Three phenotypic features that vary in pumas are the shape of the tail, the pattern of hair growth on the back and the position of the testes in male pumas. Variant forms of these phenotypic features that are normally rare occur at a high frequency in the small Florida population. These variant forms are: • bent tail • abnormal pattern of hair growth on the back • testes remain in abdomen in some male pumas. Predict, with reasons, whether these phenotypic features show a continuous or a discontinuous pattern of variation. Explain how the small size of the Florida population resulted in a high frequency of these normally rare variant forms. In 1995, eight puma females from Texas were introduced to Florida to increase the breeding success and future size of the puma population in Florida. In the next 20 years the population grew substantially. Suggest why the introduced females were taken from Texas and not from points A or B on .
9700_s22_qp_43
THEORY
2022
Paper 4, Variant 3
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MELAS syndrome is an inherited disease caused by a mutation in a gene located in mitochondrial DNA (mtDNA). All mtDNA is inherited from the mother. shows four generations of a family where several individuals are affected by MELAS syndrome. first generation second generation third generation fourth generation = unaffected female = female with MELAS syndrome = unaffected male = male with MELAS syndrome key With reference to , state and explain the evidence that MELAS syndrome is an mtDNA disease and not a disease caused by a mutation in a gene on the X chromosome. Analysis of mtDNA can show how recently species have evolved from each other. Describe the properties of mtDNA that make it suitable for the study of evolution.
9700_m19_qp_42
THEORY
2019
Paper 4, Variant 2
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The European eel, Anguilla anguilla, is a fish. The sizes of eel populations tend to remain relatively stable despite eels producing large numbers of offspring. Suggest two reasons why the population sizes of eels tend to remain relatively stable. Explain what is meant by the general theory of evolution. The generation time of a species is the mean time from one generation to the next generation . For example, the generation time of humans is about 25 years. shows a graph of the relationship between the rate of evolution and the generation time for a wide range of different species. rate of evolution generation time Describe and explain the relationship shown in . The tuatara, Sphenodon punctatus, is a reptile that is native to New Zealand. It is found nowhere else in the wild. shows a tuatara. Tuataras have a slow growth rate and can live for over one hundred years. Fossil evidence shows that there has been little morphological change in the tuatara over the last 200 million years. This is a much lower rate of evolution than would be expected from the generation time of this species. Suggest and explain why the tuatara has remained largely unchanged over the last 200 million years.
9700_m21_qp_42
THEORY
2021
Paper 4, Variant 2
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Natural selection and artificial selection (selective breeding) both have important roles in evolutionary change. Seahorses are fish with an unusual appearance and many specialised features. shows a seahorse. Two species of seahorse, Hippocampus erectus and H. zosterae, are found in the coastal waters of the Gulf of Mexico and the Caribbean Sea. • It is thought that these two species of seahorse have a common ancestor. • The ranges of the two species overlap in many areas. • Male and female seahorses stay together for the whole of the breeding season. • H. erectus is much larger than H. zosterae. • Few seahorses occur that are intermediate in size between the two species. Use this information to name and explain the type of speciation that may have occurred in the evolution of these two species. For many years, farmers have used selective breeding to improve the milk yield of dairy cattle and to improve the yield of crops. Explain why improving milk yields in cattle by selective breeding can be more challenging than improving yields of crops by selective breeding. State two examples of crop features that may be improved by selective breeding to increase the yield of crops.
9700_m22_qp_42
THEORY
2022
Paper 4, Variant 2
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Questions Discovered
104