A-LevelBiologySelection and evolution9700/41 · Oct/Nov 2021 · Q85 Marks

California salamanders are terrestrial amphibians. An original population of California salamanders occupied an area of forest in northern California. Approximately 10 million years ago, two separate populations, A and B, started to migrate from the original population. • Population A travelled along the coast of California, to the west of the Great Central Valley. • Population B travelled east of the Great Central Valley. The two populations now live close to each other in southern California. Fig. 8.1 outlines the migratory routes of populations A and B. [Figure 8.1] Salamanders from population A rarely interbreed with salamanders of population B. If they do interbreed, the offspring are infertile.

Suggest and explain the sequence of events that have resulted in these two populations becoming reproductively isolated from each other.[5]

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 (Oct/Nov 2021). The mark or mark type is shown in brackets.

[1] due to (Great Central) Valley / during migration, populations / they, are separated / geographically isolated ;
[1] no, mating / breeding / gene flow, between, them / populations ;
[1] different (named), selection pressures / environments / conditions / habitats ;
[1] different mutations ;
[1] natural selection ;
[1] genetic drift / founder effect ;
[1] change in allele frequency OR change in / different, gene pool ;
[1] leads to different, morphological / behavioural / biochemical / physiological, features ;
[1] allopatric speciation ;

On Oracle Prep you can write or photograph your own answer and have it marked by AI against this mark scheme, with feedback on what you missed.