A-LevelBiologySelection and evolution9700/41 · May/June 2022 · Q514 Marks

Two subspecies of reindeer, Rangifer tarandus, live in North America. Members of the different subspecies belong to the same species but have some morphological differences and are found in different geographical locations. [Figure 5.1] [Table 5.1]

(a)During the last ice age an ice sheet separated southern and northern populations of R. tarandus in North America. Explain how this ice sheet affected the evolution of R. tarandus to result in the two different subspecies.[4]
(b)(i)Assess the relative importance of natural selection and genetic drift in producing: the different colours of fur of the two subspecies of reindeer[2]
(b)(ii)the different body sizes of the two subspecies of reindeer.[2]
(c)Hybridisation has occurred between individuals of the two subspecies which now live in the area previously covered by the ice sheet. Comment on how the hybrid populations compare to the pure subspecies in terms of genetic variation and potential to adapt to climate change.[3]
(d)Outline how practical techniques could be used to test the hypothesis that migratory behaviour in reindeer has a genetic basis.[3]

This question uses a diagram from the original paper, which isn't shown here. Open the full paper from the past papers archive to see it.

Mark scheme

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

[4] (a) any four from: 1 geographical isolation / allopatric (sub)speciation ; 2 little / no, (inter)breeding / gene flow, between populations ; 3 different, selection / selective, pressures (on each population); 4 different mutations (in each population); 5 adaptation to, environment/ habitat / climate / food / vegetation ; 6 gives, morphological / ecological / behavioural, differences ;
[2] (b)(i) any two from: 1 natural / selection ; 2 dark, colour / fur, selected for / adaptive / good, in woods / warm / shade ; 3 camouflage / right colour, protects against, (named) predators ;
[2] (b)(ii) any two from: 1 genetic drift/ not natural selection ; 2 as small size in north not, adaptive / beneficial; 3 (small) lose heat faster / harder to keep warm ; 4 smaller fat reserves not good with unstable food supply; 5 less food in north reduces, growth / size ; 6 AVP;
[3] (c) any three from: 1 (hybrid populations have) more, genetic variation / alleles ; 2 genes / mutations / alleles, from both (sub)species ; 3 more potential to adapt / can adapt better (in future) ; 4 genes / alleles, for migration may let some find new habitats ; 5 have, genes / alleles, for, warm and cold / different temperatures ;
[3] (d) any three from: 1 obtain, blood / tissue / DNA ; 2 (test) both (sub)species / migratory and non-migratory ; 3 use PCR to amplify DNA; 4 use, (gel) electrophoresis / DNA profiling / DNA fingerprinting, and EITHER compare results OR to see genetic, differences / changes ; 5 sequence DNA and, count / identify, differences / changes ; 6 check/test, for correlation between, DNA / genetic profiles / alleles / markers, and migratory behaviour ; 7 use, databases / bioinformatics, to find, name / role of, genes / sequences (that, differ / are associated with migration); 8 AVP;