17.2. Natural and artificial selection
A subsection of Biology, 9700, through 17. Selection and evolution
Listing 10 of 69 questions
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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Use Explain what is meant by artificial selection. In a plant breeding programme, corn, Zea mays, was bred in an attempt to produce a high yield of protein in the grain. The results of this programme are shown in . mass of protein / g per 100 g of grain generations Examiner’s Use With reference to , calculate the percentage increase in grain protein by the end of the experiment. Show your working. Answer % Suggest why the protein yield does not increase steadily in each generation. Section B starts on page 22
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THEORY
2007
Paper 4, Variant 0
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The Atlantic herring, Clupea harengus, lives in large populations called shoals and may grow up to 40 cm long. shows the appearance of C. harengus. The length of C. harengus shows wide variation. shows the numbers of fish of different lengths in a population of C. harengus. The arrows show the selection pressures, P and S. length of fish / cm number of fish selection pressure P selection pressure S Sketch a graph on the axes below to show the distribution of length of C. harengus, when selection pressures P and S operate for a few years. length of fish / cm number of fish Name this type of natural selection Sketch a graph on the axes below to show the distribution of length of C. harengus, when selection pressure S alone operates for a few years. length of fish / cm number of fish Name this type of natural selection Suggest two examples of selection pressure S. 1. 2.
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THEORY
2008
Paper 4, Variant 0
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The following passage is a summary of the main principles of natural selection. Some of the words have been omitted. Write the most appropriate term in each space. Individuals in a population have great potential and yet the numbers in a population remain roughly . This is because many die due to environmental factors and therefore do not reproduce. There is amongst members of a population and those with the features best adapted to the environment survive. They reproduce and pass on their to their offspring. This may lead to a change in the pool of the population and over time may lead to evolutionary change.
9700_s11_qp_42
THEORY
2011
Paper 4, Variant 2
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The following passage is a summary of the main principles of natural selection. Some of the words have been omitted. Write the most appropriate term in each space. Individuals in a population have great potential and yet the numbers in a population remain roughly . This is because many die due to environmental factors and therefore do not reproduce. There is amongst members of a population and those with the features best adapted to the environment survive. They reproduce and pass on their to their offspring. This may lead to a change in the pool of the population and over time may lead to evolutionary change.
9700_s11_qp_43
THEORY
2011
Paper 4, Variant 3
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shows the structure of a male flower of maize, Zea mays. With reference to , explain how two features of this flower adapt it for wind pollination. The corn borer, Ostrinia nubilalis, is an insect pest of maize. The larvae are caterpillars that eat the leaves of the maize plants. The adults can fly. Adult corn borers do not feed on maize plants. Much of the maize that is grown in the USA has been genetically modified to produce Bt toxin, which is lethal to insects that feed on the leaves. However, many populations of the corn borer have now evolved resistance to the Bt toxin. Explain how this resistance could have evolved. The recessive allele, r, of the gene in corn borers confers resistance to Bt toxin. Larvae that are homozygous for the normal, dominant allele R, or that are heterozygous, are killed when they feed on Bt maize. State the genotype of the corn borers that successfully turn from larvae into adults in the fields where Bt maize is grown. In order to reduce the number of corn borers resistant to Bt toxin, farmers in the USA are required to grow up to 50% of their maize as non-Bt varieties. The non-Bt maize is grown in separate areas, called ‘refuges’, close to the fields of Bt maize. This is called the HDR strategy. Almost all corn borer larvae feeding on this non-Bt maize have the genotypes RR or Rr. The HDR strategy assumes that, when these become adults, they will interbreed with the adults developing in the Bt maize fields. Explain how the HDR strategy could reduce the proportion of corn borers that are resistant to the Bt toxin. The HDR strategy works only if a high proportion of the adult corn borers developing in the Bt fields mate with adult corn borers from the non-Bt refuges. An investigation was carried out to determine the extent to which female corn borers mate with males from their own field, or from outside that field. • Several hundred male and female adult corn borers were marked and then released into a maize field that contained no corn borers. • After 36 hours, as many corn borers as possible were recaptured from the field and the number of marked and non-marked male and female corn borers was recorded. • The percentage of the marked females that had mated with marked males was also recorded. • This was repeated on four more occasions. The results are shown in Table 4.1. Table 4.1 trial percentage of recaptured males that were marked percentage of recaptured females that were marked percentage of marked females that had mated percentage of marked females that had mated with marked males With reference to the two shaded columns in Table 4.1, explain what the results indicate about the degree of mixing between corn borers from different fields. With reference to Table 4.1, suggest and explain the implications of the results of this investigation for the effectiveness of the HDR strategy.
9700_s12_qp_41
THEORY
2012
Paper 4, Variant 1
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The seahorse, Hippocampus, is an unusual small fish. It gives birth to live young and it is the male rather than the female that becomes pregnant. shows a seahorse. In one species of seahorse, a type of natural selection called disruptive selection occurs. This is where the extreme phenotypes are more likely to survive and reproduce than the intermediate phenotypes. • Within a population, large females mate with large males and small females mate with small males. • Few intermediate-sized individuals are produced and they have a low survival rate. Sketch a graph on the axes below to show the distribution in size of seahorses as a result of disruptive selection. number of seahorses size of seahorses Explain how disruptive selection has been maintained in this species of seahorse. State the term given to the type of selection where variation in a characteristic is maintained in its existing form over time. Two different species of seahorse are found in the coastal waters shown in . Yucatan Cuba Florida Atlantic Ocean Caribbean Gulf of Mexico Louisiana L S L L S S S L L L L L L L L L L L L Key: L = large seahorse H. erectus S = small seahorse H. zosterae Suggest how these two different species of Hippocampus could have arisen.
9700_s12_qp_42
THEORY
2012
Paper 4, Variant 2
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Questions Discovered
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