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 increased significantly. Describe how natural selection resulted 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 at risk from larger predators. Fur colour in Arctic foxes is determined by genes and is inherited by offspring.
Model answer (5 marks)
There is variation in fur colour within the population – some foxes are white and some are brown.
White‑furred foxes are better camouflaged in the snowy environment, so they are less likely to be seen and eaten by predators and more likely to catch prey.
Because they survive better, white‑furred foxes are more likely to reproduce.
They pass the gene for white fur on to their offspring.
Over many generations the frequency of the white‑fur gene increases in the population.
White‑furred foxes are better camouflaged in the snowy environment, so they are less likely to be seen and eaten by predators and more likely to catch prey.
Because they survive better, white‑furred foxes are more likely to reproduce.
They pass the gene for white fur on to their offspring.
Over many generations the frequency of the white‑fur gene increases in the population.
Examiner tips
- Show the step‑by‑step chain of natural selection: variation → differential survival → differential reproduction → change in allele frequency.
- Use the exact terms: variation, better adapted, survival, reproduction, allele frequency.
- Keep the answer concise – 5 points, one sentence per point.
Common mistakes
- Mixing up ‘survival’ with ‘reproduction’ – both are needed but survival is the first step.
- Using vague words like ‘more likely’ without linking to survival or reproduction.
- Failing to mention that the change is over many generations.
Mark scheme (5 marks)
- There is variation in fur colour within the population (white and brown fur)
- White-furred foxes are better camouflaged / better adapted to the snowy environment
- White-furred foxes are more likely to survive / less likely to be predated / more likely to catch prey
- White-furred foxes are more likely to reproduce and pass on the gene/allele for white fur to offspring
- Over many generations, the frequency of the white 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 "Describe" question →
- Decode the mark scheme abbreviations →
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