A population of Arctic foxes lives in a snowy environment. Some foxes have thicker fur than others due to a mutation. Explain how natural selection could lead to most foxes in the population having thicker fur over many generations.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
Arctic foxes live in extremely cold, snowy environments. They rely on their fur for insulation. A random mutation has resulted in some individuals in the population having thicker fur than others.
Model answer (4 marks)
There is variation in fur thickness within the population because of a random mutation.
Foxes with thicker fur are better insulated, so they survive the cold better than those with thinner fur.
Because they survive, they are more likely to reproduce and pass the allele for thicker fur to their offspring.
Over many generations the frequency of the allele for thicker fur rises, so most foxes in the population end up with thicker fur.
Foxes with thicker fur are better insulated, so they survive the cold better than those with thinner fur.
Because they survive, they are more likely to reproduce and pass the allele for thicker fur to their offspring.
Over many generations the frequency of the allele for thicker fur rises, so most foxes in the population end up with thicker fur.
Examiner tips
- Show the four steps in order: variation, differential survival, differential reproduction, change in allele frequency.
- Use words like "mutation", "allele", "survive", "reproduce", "frequency".
- Keep sentences short and to the point.
Common mistakes
- Confusing survival with reproduction; students say thicker fur only helps survival but ignore reproduction.
- Using vague terms like "better" without linking to survival advantage.
- Failing to mention the mutation as the source of variation.
Mark scheme (4 marks)
- There is variation in fur thickness within the population (due to mutation)
- Foxes with thicker fur are better adapted / more suited to the cold environment and are more likely to survive
- Foxes with thicker fur are more likely to reproduce and pass on the advantageous allele to offspring
- Over many generations the frequency of the allele for thicker fur increases in the population
Key terms in this question
Related
- Revision notes: Natural selection and evolution →
- How to answer a "Explain" question →
- Decode the mark scheme abbreviations →
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