17. Selection and evolution
A section of Biology, 9700
Listing 10 of 104 questions
Russian scientists have discovered the fruits of a flowering plant, Silene stenophylla, in the food store in a burrow of a ground squirrel in frozen sediments in Siberia. Dating techniques suggest that the fruits were stored by the ground squirrel about 32 000 years ago, shortly before the ground became permanently frozen. Tissue samples were taken from the fruits and grown in a nutrient culture medium. After treatment with plant hormones to stimulate the growth of roots and shoots, 36 complete plants were produced. These ‘regenerated’ plants, which looked identical to one another, flowered and after cross-pollination, produced seeds that were able to germinate. Explain why cross-pollination produces more genetic variation among the offspring than self-pollination. The flowers of modern-day S. stenophylla look similar, but not identical, to the flowers of the ‘regenerated’ plants. Outline how DNA sequencing could be used to compare the DNA of modern-day and ‘regenerated’ S. stenophylla. Suggest a simple experiment, using plants of modern-day and ‘regenerated’ S. stenophylla to find out whether, after 32 000 years, they are still the same species.
9700_s14_qp_43
THEORY
2014
Paper 4, Variant 3
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Bison are a type of large wild cattle. Ancestors of modern bison appeared in Asia 2.5 million years ago. This ancestral bison species increased its range into Europe and North America. While the ancestral species is now extinct, its descendants include Bison bonasus, the European bison, and Bison bison, the American bison. shows an American bison. After the end of the last ice age, populations of the ancestral bison were separated by sea and by forests that were not suitable as habitats. The separation resulted in the evolution of the European bison and the American bison. Explain how this separation resulted in the evolution of the two bison species. Table 5.1 compares features of European bison and American bison. Table 5.1 feature European bison, B. bonasus American bison, B. bison type of food grass and higher vegetation such as leaves of bushes and trees grass and low vegetation height / m 2.1 2.0 maximum mass / kg Assess the relative importance of natural selection and genetic drift in producing the different heights and masses of the two species of bison. The European bison has a nuclear genome that is very similar to that of the American bison. The European bison has a mitochondrial genome that is more similar to that of wild cattle of the genus Bos than to the American bison. Discuss what this implies about the evolutionary history of the European bison. Outline how practical techniques could be used to test the hypothesis that farmed cattle are closely related to European bison.
9700_s22_qp_42
THEORY
2022
Paper 4, Variant 2
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DNA barcoding is used in species identification. To create a DNA barcode, a specific region of DNA is sequenced so that it can be compared to an online database of reference DNA. One region of DNA that is commonly used is 648 base pairs long within a mitochondrial gene, coding for the enzyme cytochrome c oxidase I. The solitary sandpiper, Tringa solitaria, is a migratory bird. DNA barcoding has shown that approximately 2.5 million years ago T. solitaria evolved into two subspecies, Tringa solitaria solitaria and Tringa solitaria cinnamomea. A subspecies is a genetically distinct population of a species that has some phenotypic differences but is not yet reproductively isolated. T. s. solitaria breed in eastern North America whereas T. s. cinnamomea breed in western North America. Suggest and explain how the two subspecies T. s. solitaria and T. s. cinnamomea could have evolved from the original T. solitaria population. shows an American oystercatcher, Haematopus palliatus. The black oystercatcher, Haematopus bachmani, has all black feathers. DNA barcoding analysis suggests that the American oystercatcher and the black oystercatcher are not separate species. Suggest how DNA barcoding evidence could indicate that the American oystercatcher and black oystercatcher are not separate species. Customs officers at airports can use a hand-held DNA barcoding device to identify biological specimens entering or leaving a country. Suggest how this helps protect endangered species.
9700_w20_qp_41
THEORY
2020
Paper 4, Variant 1
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DNA barcoding is used in species identification. To create a DNA barcode, a specific region of DNA is sequenced so that it can be compared to an online database of reference DNA. One region of DNA that is commonly used is 648 base pairs long within a mitochondrial gene, coding for the enzyme cytochrome c oxidase I. The solitary sandpiper, Tringa solitaria, is a migratory bird. DNA barcoding has shown that approximately 2.5 million years ago T. solitaria evolved into two subspecies, Tringa solitaria solitaria and Tringa solitaria cinnamomea. A subspecies is a genetically distinct population of a species that has some phenotypic differences but is not yet reproductively isolated. T. s. solitaria breed in eastern North America whereas T. s. cinnamomea breed in western North America. Suggest and explain how the two subspecies T. s. solitaria and T. s. cinnamomea could have evolved from the original T. solitaria population. shows an American oystercatcher, Haematopus palliatus. The black oystercatcher, Haematopus bachmani, has all black feathers. DNA barcoding analysis suggests that the American oystercatcher and the black oystercatcher are not separate species. Suggest how DNA barcoding evidence could indicate that the American oystercatcher and black oystercatcher are not separate species. Customs officers at airports can use a hand-held DNA barcoding device to identify biological specimens entering or leaving a country. Suggest how this helps protect endangered species.
9700_w20_qp_43
THEORY
2020
Paper 4, Variant 3
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Questions Discovered
104