A-LevelBiologySelection and evolution9700/42 · Feb/Mar 2022 · Q19 Marks

The European hedgehog, Erinaceus europaeus, is a small omnivorous mammal. Its body is covered in spines, which are usually brown. A rare variant, which lacks the brown pigment, has blonde (pale yellow) spines. This characteristic is coded for by a recessive allele. Fig. 1.1 shows a European hedgehog with blonde spines. [Figure 1.1]

(a)Alderney is a small island between the UK and France. Hedgehogs were not found on Alderney until the 1960s, when three pairs of hedgehogs were introduced to the island. The hedgehogs started to breed and some of the offspring had blonde spines. By 2017, the population of hedgehogs, including individuals with brown spines and individuals with blonde spines, had increased to approximately 600. (i) Suggest reasons why the population of hedgehogs increased to such a large number.[2]
(a)(ii)A survey taken in 2017 showed that 60% of the hedgehogs on Alderney had blonde spines. Suggest and explain reasons why the proportion of hedgehogs with blonde spines was so high.[3]
(b)The hedgehogs on Alderney are an example of an invasive alien species. Explain why it is sometimes important to control invasive alien species.[4]

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Mark scheme

Marking points from the official mark scheme (Feb/Mar 2022). The mark or mark type is shown in brackets.

[2] any two from: 1 high birth rate / short generation time / AW ; 2 few/no, predators ; 3 little competition; 4 plenty of food available / wide range of food types eaten / omnivore ; 5 no/fewer, diseases ; 6 well adapted / no selection pressures against them; A description
[3] any three from: 1 directional selection; 2 blonde spines have a selective advantage / described / AW ; 3 allele frequency for blonde spines increases / increased homozygosity (for recessive or blonde allele); 4 inbreeding; 5 small gene pool (at start) / little genetic variation ; 6 founder effect / genetic drift / bottleneck effect ; A description
[4] any four from: accept local for native throughout because alien species: 1 compete with native species ; 2 for, food/ same niche / light/resources or reduce food source of native species ; 3 feed on / predators of, native species ; 4 can cause extinction in native species; 5 can breed more successfully than native species ; 6 often have no, natural predator / grazers ; 7 may disrupt, habitats / ecosystems / food webs / food chains ; ignore environment 8 cause reduction in biodiversity ; 9 may introduce disease ;

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