Explain how natural selection could lead to a population of rock pocket mice living on dark volcanic rock becoming mostly dark-coloured over many generations, starting from a population that is mostly light-coloured.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
Rock pocket mice live on rocky ground in North America. They are preyed upon by owls and other birds of prey that hunt by sight. In one region, a volcanic lava flow has created an area of dark rock. A population of mostly light-coloured rock pocket mice has moved into this area.
Model answer (4 marks)
Variation in coat colour exists in the population – some mice are dark, some light, caused by mutation.
Light‑coloured mice are more visible against the dark volcanic rock and are more likely to be eaten by predators.
Dark‑coloured mice are better camouflaged, survive and reproduce more successfully, passing the allele for dark colouration to their offspring.
Over many generations the frequency of the dark‑colour allele rises, so the population becomes mostly dark‑coloured.
Light‑coloured mice are more visible against the dark volcanic rock and are more likely to be eaten by predators.
Dark‑coloured mice are better camouflaged, survive and reproduce more successfully, passing the allele for dark colouration to their offspring.
Over many generations the frequency of the dark‑colour allele rises, so the population becomes mostly dark‑coloured.
Examiner tips
- Use the word ‘variation’ to show genetic diversity. Explain the selective advantage of camouflage. Show the link between survival, reproduction and allele frequency. Mention ‘over many generations’ to indicate time.
- common_mistakes
- :
- Failing to state that variation exists. Confusing the direction of selection (light mice surviving). Not linking survival to allele frequency change.
Mark scheme (4 marks)
- There is variation in coat colour within the population / some mice are dark-coloured and some are light-coloured, due to mutation
- Light-coloured mice are more visible on dark rock and are more likely to be eaten by predators / dark-coloured mice are better camouflaged and less likely to be eaten
- Dark-coloured mice are more likely to survive, reproduce and pass on the gene/allele for dark colouration to their offspring
- Over many generations the frequency of the allele for dark colouration increases in the population / the proportion of dark-coloured mice in the population increases
Key terms in this question
Related
- Revision notes: Evolution by natural selection →
- How to answer a "Explain" question →
- Decode the mark scheme abbreviations →
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