17. Selection and evolution
A section of Biology, 9700
Listing 10 of 104 questions
Scientists have found very little evolutionary change in populations of two Australian songbirds, the zebra finch, Taeniopygia guttata castanotis, and the budgerigar, Melopsittacus undulatus. Describe the process of evolution by natural selection. The number of eggs a bird lays in its nest is called the clutch size. The variation in clutch size was investigated in the zebra finch over several years. The data are shown in . clutch size number of clutches Describe the pattern shown by the data in . The data in this investigation were collected over 60 years ago. The same investigation, carried out today, would produce the same pattern of results. Explain how the selection factors acting on zebra finches would maintain the same pattern of results. The Hardy–Weinberg principle is used to calculate allele, genotype and phenotype frequencies in populations. • A breeder of birds keeps a population of 86 budgerigars in one enclosed area. • Two distinct phenotypes are present, blue feathers and green feathers. • Feather colour is controlled by one gene: G is the allele for green feathers g is the allele for blue feathers. • Only 17 of the budgerigars have blue feathers. The Hardy–Weinberg equations are shown in . p + q = 1 p2 + 2pq + q2 = 1 Calculate the number of heterozygous individuals in the population. Show your working. number = The Hardy–Weinberg principle cannot be applied to all populations. State two conditions when the Hardy–Weinberg principle cannot be applied.
9700_s18_qp_41
THEORY
2018
Paper 4, Variant 1
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A study was carried out to investigate natural selection in the plant evening primrose, Oenothera biennis. Physiological changes associated with resistance to grazing by herbivorous insects were measured over 5 years in 16 experimental populations of evening primrose. For 8 of the experimental populations the plants were regularly sprayed with chemical insecticide, and the other 8 experimental populations were not sprayed. In each of the 5 years some older plants died after producing seeds and some new plants grew from seed. Observations after the study were: • sprayed populations: The length of time that the plants produced flowers (flowering period) became longer. Flowering started earlier in each generation. The mean concentration of natural insect-deterring chemicals in the plants was relatively low. • non-sprayed populations: The flowering period remained the same over the 5 years. The mean concentration of natural insect-deterring chemicals in the plants increased. Analysis showed that genetic differences were responsible for the differences in flowering time and concentration of natural insect-deterring chemicals in the plants. The researchers concluded that natural selection was acting on both groups of plants. Explain how natural selection acted in the non-sprayed populations to cause the mean concentration of natural insect-deterring chemicals to increase. Identify the type of natural selection that caused an increase in the mean concentration of insect-deterring chemicals in the non-sprayed populations. Identify the type of natural selection that caused the flowering period to remain the same in the non-sprayed populations. The same trends in results were recorded in all of the non-sprayed populations. Explain how this supports the researchers’ conclusion that natural selection caused the trends and not genetic drift.
9700_s18_qp_43
THEORY
2018
Paper 4, Variant 3
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Researchers investigated the extent to which the founder effect and natural selection affected evolutionary change. shows the brown anole lizard, Anolis sagrei. These lizards live on a number of Caribbean islands and feed on a variety of invertebrates and other small animals. perch diameter A. sagrei spends a lot of time perching on, or moving along, branches of shrubs and trees. The width of the branch that A. sagrei perches on is known as the perch diameter, as labelled in . There is a positive correlation between perch diameter and hind limb length of A. sagrei. • Longer hind limbs allow A. sagrei to run faster on vegetation with a larger diameter. • Shorter hind limbs are needed to provide stability on vegetation of a smaller diameter. In 2004, a hurricane caused the death of all the A. sagrei lizards on seven islands. In 2005, the researchers randomly collected seven male and seven female lizards from a source population on a nearby island. For each of the seven islands affected by the hurricane, a male and female lizard were mated and placed on each island. These islands formed the experimental founder islands where new populations of A. sagrei were successfully established from each founding pair. shows the difference in vegetation between the source island and the seven experimental founder islands. source population experimental founder islands Predict the effect of natural selection on mean hind limb length of A. sagrei on the seven experimental founder islands. Predict how collecting individuals at random for the seven founding pairs affects the mean hind limb length of A. sagrei on the different islands. Many generations of A. sagrei were produced over the four years after the introduction of the founding pairs. shows how the mean hind limb length of A. sagrei changed on the seven experimental islands and on the source island. year mean hind limb length Key: source island island 1 island 2 island 3 island 4 island 5 island 6 island 7 With reference to and , describe and suggest explanations for the results for the islands. In the investigation, one population of A. sagrei was established on each experimental founder island. Outline how speciation may occur on the seven experimental founder islands. Speciation is one possible outcome for the experimental founder populations, but there is also a high risk that they may become extinct. Explain why the experimental founder populations are at high risk of extinction.
9700_s19_qp_41
THEORY
2019
Paper 4, Variant 1
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Regressive evolution is a change in a population over time that involves the loss of certain phenotypic characteristics. It is thought to be caused by either genetic drift or natural selection. An example of regressive evolution is the loss of eyes in one form of the Mexican cavefish, Astyanax mexicanus. These eyeless cavefish live in caves that are in total darkness. There are three theories to explain how the loss of eyes in the cavefish has occurred. Theory A There is no advantage to having eyes in a cave that is in total darkness, where energy sources are scarce. Having eyes is a disadvantage as there may be an energy cost. Theory B A mutation has occurred in a single gene. This mutation has two effects: • a lack of eye development • an increase in the number of chemoreceptors on the skin. Theory C Various mutations occurred in the genes responsible for eye development over a period of time. By chance, these mutations increased in frequency in small isolated populations. Eventually this produced a population of eyeless cavefish. State one theory, A, B or C, which describes genetic drift as the cause of loss of eyes. State and explain which theory or theories are based on natural selection as the cause of loss of eyes. There are several separate populations of eyeless A. mexicanus in different caves. There are populations of A. mexicanus that spend time in areas with light and the fish in these populations have eyes. The mitochondrial DNA (mtDNA) of eyeless A. mexicanus was compared to the mtDNA of A. mexicanus with eyes. Suggest how DNA evidence can help find out whether the eyeless A. mexicanus and the A. mexicanus with eyes are the same species or different species. Suggest why mtDNA is used instead of nuclear DNA when studying the closeness of the relationship between populations.
9700_s19_qp_43
THEORY
2019
Paper 4, Variant 3
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The collared flycatcher, Ficedula albicollis, and the pied flycatcher, F. hypoleuca are two closely related species of bird. DNA analysis has shown that speciation from a common ancestor occurred approximately 1 million years ago. A study was carried out on the island of Öland, Sweden. In Öland, the breeding areas of the two bird species overlap and small numbers of hybrid flycatchers are produced. • Birds were captured and their DNA was analysed to identify whether each bird was F. albicollis, F. hypoleuca or a hybrid. • Sperm samples were taken from the male birds. Table 3.1 shows the percentage of males of each bird type with normal sperm. Table 3.1 bird type percentage of males with normal sperm F. albicollis F. hypoleuca male hybrid • The researchers observed that female birds mostly choose mates of their own species based on plumage and song. • Hybrid flycatchers are produced when female F. albicollis mate with male F. hypoleuca that have a song that is similar to F. albicollis. • Analysis showed that all female hybrids were sterile. The group of eggs a female bird lays at a single time in its nest is called a clutch. The offspring in the nest are looked after by a male-female pair. Sometimes the male in the male-female pair does not provide the sperm that fertilise the eggs of the female. Table 3.2 shows: • the percentage of clutches with eggs that hatched • the percentage of extra-pair nestlings (offspring in the nest fathered by a male that was different from the male of the male-female pair). Table 3.2 parents of nest percentage of clutches with eggs that hatched percentage of extra-pair nestlings male female F. albicollis F. albicollis 94.5 17.2 F. hypoleuca F. hypoleuca 89.3 22.4 hybrid F. albicollis or F. hypoleuca 38.0 100.0 Discuss the pre-zygotic and post-zygotic isolating mechanisms that maintain F. albicollis and F. hypoleuca as separate species. Explain how the two species F. albicollis and F. hypoleuca could have evolved from one original ancestral population. A single-nucleotide polymorphism (SNP) is caused by a base pair substitution mutation in a specific region of DNA. One method of identifying whether two individuals have the same SNP is to: • use a specific primer and polymerase chain reaction (PCR) • add a restriction enzyme • carry out gel electrophoresis • stain with a dye to compare banding patterns. Explain why: a specific primer is used a restriction enzyme is added gel electrophoresis is carried out. The method of identifying whether two individuals have the same SNP method was carried out to compare species A and species B. shows the banding patterns that were observed. A species B well well Describe and suggest an explanation for the results obtained in .
9700_s20_qp_43
THEORY
2020
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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Questions Discovered
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