18.3. Selection
A subsection of Biology, 0610, through 18. Variation and selection
Listing 10 of 88 questions
Characteristics of plants are controlled by genes. Alleles are alternative forms of a gene. Explain how new alleles are formed. The number of hours of daylight affects when plants produce flowers. This ensures that flowers are produced at an appropriate time of year for each species. This response to the number of hours of daylight is controlled by genes. Wheat is a crop plant. A farmer wants to produce a type of wheat that flowers when there are fewer hours of daylight. Describe how the farmer could selectively breed this type of wheat. Wheat is grown from seeds. State two conditions needed for the germination of seeds. Different types of wheat have also evolved through natural selection. Explain how natural selection differs from artificial selection. Scientists can selectively breed for increased pest resistance in wheat. Explain the benefits of growing wheat with increased pest resistance.
0610_s24_qp_43
THEORY
2024
Paper 4, Variant 3
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For Examiner's Use Reed warblers are small birds that migrate over long distances between western Africa and northern Europe. shows a reed warbler, Acrocephalus scirpaceus. State three characteristic features of birds that are visible in . A study was carried out in Sweden into the effects of natural selection on wing length in reed warblers. The wings of young reed warblers reach their maximum length a few days after leaving the nest. At this age the wing length in millimetres of each bird was recorded. Each bird was identified by putting a small ring around one of its legs. When the birds were caught in net traps as adults, the information on the rings was used to identify specific birds and their ages. For Examiner's Use The length of time between ringing and trapping was recorded for each bird that was identified before it was released. The mean age at trapping was calculated for birds with each wing length. The results are shown in Table 5.1. Table 5.1 wing length at ringing / mm number of birds trapped mean age at trapping / days 63 or less 70 or more total = 771 Explain why wing length is an example of continuous variation. Suggest a feature of reed warblers, other than wing length, that shows continuous variation. For Examiner's Use The researchers concluded that reed warblers with a wing length of 66-67 mm had the best chance of survival. Describe the evidence from Table 5.1 that supports this conclusion. The researchers also suggested that more evidence was needed to make this conclusion. Suggest what other evidence would show that birds with wings 66-67 mm in length have the best chance of survival. For Examiner's Use Scientists have discovered that genes are responsible for wing length in reed warblers. The most common length of wing has been 66-67 mm for many generations of these birds. Explain how natural selection may be responsible for maintaining the mean wing length of reed warblers at 66-67 mm.
0610_w11_qp_32
THEORY
2011
Paper 3, Variant 2
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For Examiner's Use shows Soay sheep on St. Kilda, a group of small remote islands off the coast of Scotland. These islands experience extreme conditions of cold, wind and rain. Sheep were introduced to the islands thousands of years ago and the Soay sheep are descended from them. The islands of St. Kilda have been uninhabited by people since 1930. The sheep are now left unfarmed and in their natural state. The populations of Soay sheep on St. Kilda show much more variation in their phenotype than modern breeds of sheep. Explain, by using an example from , what is meant by variation in their phenotype. For Examiner's Use Scientists have recorded the numbers of Soay sheep and lambs on St. Kilda for many years. Each year between 1985 and 1996, the lambs (young sheep) were caught, marked and weighed. In some years, the total number of sheep on St. Kilda was lower than in other years. shows the frequency of lambs of different body mass in years when the total number of sheep was low and years when the total number was high. frequency of lambs 3–4 5–6 7–8 9–10 11–12 body mass / kg low population years 13–14 15–16 17–18 19–20 21–22 frequency of lambs 3–4 5–6 7–8 9–10 11–12 body mass / kg high population years 13–14 15–16 17–18 19–20 21–22 key lambs that died lambs that survived for at least a year For Examiner's Use Population size has a great effect on the survival of lambs on St. Kilda. Describe the evidence from that supports this statement. Suggest an explanation for the effect that you have described. Soay sheep are adapted to the extreme conditions experienced on St. Kilda. Explain how natural selection could account for the adaptive features of Soay sheep.
0610_w13_qp_32
THEORY
2013
Paper 3, Variant 2
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Apple scab is a disease that infects apple trees. shows apples from uninfected and infected apple trees. uninfected apple tree infected apple tree There is a gene that determines whether or not apple trees are resistant to apple scab disease. There are two alleles for this gene: • disease-resistant, R • not disease-resistant, r Complete the sentence. Genes and alleles are made of . A farmer wanted to do a test cross to identify the genotype of disease-resistant apple trees. This would tell him whether his trees were either homozygous dominant or heterozygous. Determine the phenotypes of the offspring if the unknown parent apple tree was heterozygous. Complete the genetic diagram: parental phenotypes disease-resistant × not disease-resistant parental genotypes × gametes , × , offspring genotype offspring phenotype The farmer wanted to breed disease-resistant apple trees. He decided not to use heterozygous disease-resistant apple trees in his selective breeding programme. Explain why. The farmer wanted to be sure that only the selected disease-resistant apple trees would reproduce. Suggest what the farmer could do to ensure that only the selected apple trees were pollinated. Describe how artificial selection differs from natural selection.
0610_w17_qp_43
THEORY
2017
Paper 4, Variant 3
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Questions Discovered
88