A population of rock pocket mice lives in a desert environment where the ground is covered in pale sand. The mice have a variety of fur colours, ranging from pale to dark. Explain how, over many generations, natural selection could lead to the population consisting mainly of pale-furred mice.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
Rock pocket mice are small rodents that are preyed upon by owls and hawks. Individual mice vary in fur colour due to differences in their genes. Pale-furred mice blend in with pale sandy ground, whilst dark-furred mice are more easily spotted by predators.
Model answer (5 marks)
There is variation in fur colour within the population of rock pocket mice.
Pale‑furred mice are better camouflaged in the pale sandy environment.
Because they are less likely to be eaten by predators, pale‑furred mice have a greater chance of survival.
They are therefore more likely to reproduce and pass on the genes for pale fur to their offspring.
Over many generations the frequency of the pale‑fur gene increases in the population, so the population consists mainly of pale‑furred mice.
Pale‑furred mice are better camouflaged in the pale sandy environment.
Because they are less likely to be eaten by predators, pale‑furred mice have a greater chance of survival.
They are therefore more likely to reproduce and pass on the genes for pale fur to their offspring.
Over many generations the frequency of the pale‑fur gene increases in the population, so the population consists mainly of pale‑furred mice.
Examiner tips
- Use the exact sequence of points from the mark scheme
- Show the causal chain: variation → better adaptation → survival → reproduction → change in allele frequency
- Keep sentences short and to the point
Common mistakes
- Failing to mention the initial variation in fur colour
- Confusing ‘survival’ with ‘reproduction’ or omitting the link to gene transmission
- Using vague terms like ‘more likely’ without linking to natural selection
Mark scheme (5 marks)
- There is variation in fur colour within the population of rock pocket mice
- Pale-furred mice are better camouflaged / better adapted to the pale sandy environment
- Pale-furred mice are less likely to be eaten by predators / have a greater chance of survival
- Pale-furred mice are more likely to reproduce and pass on the genes for pale fur to offspring
- Over many generations, the frequency of the pale fur gene / allele increases in the population
Key terms in this question
Related
- All Edexcel A-Level Biology A: Salters-Nuffield (9BN0) revision notes →
- How to answer a "Explain" question →
- Decode the mark scheme abbreviations →
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