A population of Arctic foxes has individuals with either thick fur or thin fur. Explain how natural selection could result in thick fur becoming more common in the population over many generations, if the environment becomes colder.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
Arctic foxes live in extremely cold environments. Within a population, some individuals have thick fur and some have thin fur. This variation is caused by mutations in the genes that control fur thickness.
Model answer (4 marks)
1. There is variation in fur thickness within the population – some foxes have thick fur and some have thin fur.
2. In a colder environment, foxes with thick fur are better suited, as they retain heat more effectively and are more likely to survive.
3. Those foxes with thick fur are more likely to survive and reproduce, passing the allele for thick fur to their offspring.
4. Over many generations, the allele for thick fur increases in frequency, so thick fur becomes more common in the population.
2. In a colder environment, foxes with thick fur are better suited, as they retain heat more effectively and are more likely to survive.
3. Those foxes with thick fur are more likely to survive and reproduce, passing the allele for thick fur to their offspring.
4. Over many generations, the allele for thick fur increases in frequency, so thick fur becomes more common in the population.
Examiner tips
- Use the exact terms ‘variation’, ‘better suited’, ‘survive and reproduce’, ‘allele frequency increases’.
- Show the causal chain: variation → differential survival → differential reproduction → change in allele frequency.
Common mistakes
- Confusing ‘survival’ with ‘reproduction’ – both are needed.
- Using vague phrases like ‘more likely’ without linking to allele frequency.
Mark scheme (4 marks)
- There is variation in fur thickness within the population / some foxes have thick fur and some have thin fur
- In a colder environment, foxes with thick fur are better suited / have an advantage / are more likely to survive
- Foxes with thick fur are more likely to survive and reproduce / pass on the allele for thick fur to their offspring
- Over many generations, the allele for thick fur increases in frequency in the population / thick fur becomes more common
Key terms in this question
Related
- All WJEC GCSE Biology (Wales) revision notes →
- How to answer a "Explain" question →
- Decode the mark scheme abbreviations →
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