17.2. Natural and artificial selection
A subsection of Biology, 9700, through 17. Selection and evolution
Listing 10 of 69 questions
Explain what is meant by stabilising selection. shows the distribution of fur colour in a population of mice. The colour of the soil where the mice lived was mid‑brown. white numbers in population light brown mid- brown fur colour dark brown black Suggest why mice with white fur and mice with black fur were present in the lowest numbers in . An environmental event caused the colour of the soil to change to dark brown. On , sketch a curve to show the distribution of fur colour in the mouse population after many generations. Explain what is meant by genetic drift.
9700_s21_qp_43
THEORY
2021
Paper 4, Variant 3
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The sea blush, Plectritis congesta, is a flowering plant that grows on the west coast of North America. Individual sea blush plants produce fruit that is either winged or wingless. Investigations have shown that this characteristic is controlled by a single gene with two alleles: • a dominant winged fruit allele • a recessive wingless fruit allele. shows the difference in structure between winged fruit and wingless fruit phenotypes. 2 mm winged fruit wingless fruit A large sample of sea blush fruits was collected and their fruit-wing characteristic was recorded. Name the type of variation that is shown for the fruit-wing characteristic of the sea blush. Different sea blush plants can have fruit with different colours. Suggest two ways in which a new fruit colour could naturally occur in a sea blush population. Early taxonomists classified sea blush plants with winged fruits as a different species to sea blush plants with wingless fruits. Since this time, evidence from observations and experiments has confirmed that the plants belong to the same species. Suggest three examples of the evidence obtained that helped to confirm that these sea blush plants belong to the same species. Natural selection occurs in populations, such as in populations of sea blush plants. Explain why natural selection occurs in populations.
9700_s23_qp_42
THEORY
2023
Paper 4, Variant 2
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Warfarin is a poison used to kill rats. Some rats are resistant to warfarin and can survive the effects of the poison. Warfarin resistance is due to a mutant dominant allele at a single gene locus. Researchers investigated the population of brown rats on a large island where there are no predators of rats. On this island, warfarin is used to try to control the rat population. The researchers found that 40% of the population of rats was resistant to warfarin. Use Hardy–Weinberg equation 1 and equation 2 to calculate the percentage of the population of rats on the island that is heterozygous for warfarin resistance. equation 1 p + q = 1 equation 2 p2 + 2pq + q2 = 1 Show your working. answer % In natural populations, it is usual to find that only some of the conditions of the Hardy–Weinberg principle are met. Suggest and explain which of the conditions of the Hardy–Weinberg principle are most likely to be met for the island population of brown rats. Dominant advantageous alleles and recessive advantageous alleles both naturally occur in populations. Explain why, when a new dominant advantageous allele occurs, its frequency increases more quickly in the population than when a new recessive advantageous allele occurs.
9700_s23_qp_42
THEORY
2023
Paper 4, Variant 2
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[T • There are over 40 Galapagos Islands including the small and isolated island named Daphne Major. • Only two species of Darwin finches are found on this island. • Studies were made every year from 1970 to 1989 on the beak size of the island’s population of ground finch, Geospiza fortis, by measuring the beak length of every bird (). Larger finches with larger beaks are better at opening large seeds. From 1976 to 1978 there was a drought and only 15% of the ground finches survived and these did not breed during drought years. • All finches were reduced in number. The most conspicuous feature of the survivors of the drought years was their large beak size. • The main environmental consequences of drought is the decline in food supply, mainly seeds. During normal years, many grasses and herbs produce an abundance of small seeds. A few other plants produce a much smaller number of large seeds which are not normally eaten. Describe how environmental factors appear to have acted, during drought years, on the beak size of finches as an evolutionary force of natural selection. Finches with small beaks were found to be smaller than finches with larger beaks. Explain the stabilizing force of natural selection on the beak size and size of birds in normal years. Use Outline the mechanisms that may have let natural selection lead to the evolution of the thirteen species of Darwin finches now found on the Galapagos Islands. [Total : 8]
9700_w05_qp_4
THEORY
2005
Paper 4, Variant 0
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Use Asellus aquaticus is a small freshwater crustacean. 200 A. aquaticus were released into a pond where there had previously been none. The pond was favourable for their growth and reproduction. Describe and explain the expected changes in the population size of A. aquaticus over the following few months. In order for natural selection to occur a population must show phenotypic variation. Explain why variation is important in natural selection.
9700_w09_qp_41
THEORY
2009
Paper 4, Variant 1
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From 1975 to 1977 one of the Galapagos Islands, Daphne Major, experienced a severe drought. A ground finch, Geospiza fortis, feeds on seeds on Daphne Major. shows the ground finch, G. fortis. • One of the few plants that survived the drought produced large seeds inside tough fruits. • Many G. fortis died during the drought and the population declined from 1400 in 1975 to 190 in 1977. • The mean beak depth of those G. fortis that died was 10.68 mm and the mean beak depth of those that survived was 11.07 mm. • The mean beak depth of G. fortis before the drought was 10.86 mm. Calculate the percentage decrease in population size between the years 1975 and 1977. Show all the steps in your calculation and give your answer to the nearest whole number. Answer % Suggest why some G. fortis were able to survive the drought while others died. Natural selection was taking place on Daphne Major. State the type of natural selection operating on G. fortis during the drought and explain your answer. type of natural selection explanation
9700_w10_qp_43
THEORY
2010
Paper 4, Variant 3
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The following passage is a summary of the main principles of artificial selection. Some of the words have been omitted. Write the most appropriate term in each space. When humans purposefully apply selection to members of a population, the process is known as artificial selection. For example, people have tried to ‘improve’ their cattle for thousands of years. It is desirable for a dairy farmer to have cows with a high milk yield. The farmer will select cows with high milk yields and mate them with bulls whose have high milk yields. Some of the conferring high milk yield are passed onto their female offspring who are then chosen for breeding. This will continue for many . Artificial selection can have disadvantages such as depression which can lead to infertility.
9700_w11_qp_43
THEORY
2011
Paper 4, Variant 3
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Questions Discovered
69