A population of Arctic foxes living in a snowy environment includes individuals with white fur and individuals with brown fur. Over many generations, the proportion of white-furred foxes in the population increases. Describe how natural selection results in this change in the population.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
Arctic foxes live in snowy environments where they hunt prey and are also hunted by predators. A mutation can cause some foxes to be born with white fur instead of brown fur.
Model answer (5 marks)
There is variation in fur colour within the population – some foxes are white and some are brown.
White fur gives the foxes camouflage in the snowy environment, so the white‑furred individuals are better adapted.
Because of this camouflage white‑furred foxes are less likely to be seen by predators (or are better hunters), so they survive at a higher rate.
The surviving white‑furred foxes are more likely to reproduce and pass on the allele for white fur to their offspring.
Over many generations the proportion of white‑furred foxes in the population increases as more individuals inherit the advantageous allele.
White fur gives the foxes camouflage in the snowy environment, so the white‑furred individuals are better adapted.
Because of this camouflage white‑furred foxes are less likely to be seen by predators (or are better hunters), so they survive at a higher rate.
The surviving white‑furred foxes are more likely to reproduce and pass on the allele for white fur to their offspring.
Over many generations the proportion of white‑furred foxes in the population increases as more individuals inherit the advantageous allele.
Examiner tips
- Use the exact terms: variation, adaptation, survival, reproduction, allele. Show the causal chain: variation → advantage → survival → reproduction → change in frequency. Keep each point brief and to the point to hit the 5 marks.
Common mistakes
- Mixing up the roles of predators and prey. Using vague words like ‘better’ without linking to camouflage or survival. Omitting the step that the allele is passed to offspring.
Mark scheme (5 marks)
- There is variation in fur colour within the population (white and brown fur)
- White fur provides camouflage in the snowy environment, so white-furred foxes are better adapted
- White-furred foxes are less likely to be seen by predators (or are better hunters), so are more likely to survive
- White-furred foxes are more likely to reproduce and pass on the allele/gene for white fur to offspring
- Over many generations, the proportion of white-furred foxes in the population increases as more individuals inherit the advantageous allele
Key terms in this question
Related
- All Pearson Edexcel A-Level Biology A (9BI0) revision notes →
- How to answer a "Describe" question →
- Decode the mark scheme abbreviations →
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