A-LevelBiologySelection and evolution9700/41 · May/June 2024 · Q78 Marks

It has been hypothesised that the mutation rate of an animal species may affect how fast animals of that species age and how long they live (lifespan). Table 7.1 compares the mutation rate and lifespan of five species of mammal. Table 7.1 species mutation rate per million base pairs per year mean lifespan /years cattle 0.08 20 ferret 0.20 8 horset0.05 30 human 0.02 75 house mouse 0.28 3.6

(a)(i)Describe the relationship shown in Table 7.1.[1]
(a)(ii)Use Table 7.1 to explain how these species may differ in the rate at which they can adapt if environmental selection pressures change.[3]
(b)(i)Compare the timescales needed for selective breeding and genetic engineering to increase the frequency of a rare allele in cattle. Give a reason for your answer.[2]
(b)(ii)Genetic engineering could be used to improve farmed animals, such as dairy cattle. State two features of dairy cattle that could be improved by genetic engineering.[2]

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Mark scheme

Marking points from the official mark scheme (May/June 2024). The mark or mark type is shown in brackets.

[1] (a)(i) as mutation rate increases lifespan decreases ;
[1] (a)(ii) high(er) mutation rate gives more, genetic diversity / genetic variation / alleles / chance of beneficial allele ;
[1] (a)(ii) short(er) lifespan gives more generations (per year / per unit time);
[1] (a)(ii) with, high(er) mutation rate / short(er) lifespan, they, adapt / evolve, better / more easily / faster ;
[1] (a)(ii) mouse (and ferret) may, adapt / evolve, faster ;
[1] (a)(ii) AVP ;
[1] (b)(i) comparison: C1 genetic engineering faster / selective breeding slower ;
[1] (b)(i) any one reason from: R2 selective breeding occurs over (many) generations ;
[1] (b)(i) R3 all cows could be surrogate mothers for engineered embryos (giving large increase in allele frequency in one generation) ;
[1] (b)(i) R4 AVP ;
[1] (b)(ii) (improve named) quality of, animal / milk;
[1] (b)(ii) (improve) quantity / yield, of milk ;
[1] (b)(ii) AVP;

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