Explain why the genetic diversity of a population of cheetahs is likely to be much lower than that of a population of leopards of a similar size.

OCR A-Level Biology A (H420) — 6.6 Populations and sustainability · Explain · 4 marks · View as Markdown

Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).

Cheetahs are thought to have passed through a severe population bottleneck approximately 10,000 years ago, reducing the global population to a very small number of individuals. Leopard populations have remained comparatively large and stable throughout recent evolutionary history.

Model answer (4 marks)

The bottleneck event drastically reduced the number of individuals in the cheetah population.
Only a small, non‑representative sample of alleles from the original population survived the bottleneck.
The subsequent cheetah population expanded from this genetically restricted founder group, so it lacks allelic variety.
Leopard populations remained large, maintaining a wide range of alleles through continued random mating across a large gene pool.

Examiner tips

Use the word ‘bottleneck’ early to show understanding of the event. Show the causal chain: small population → loss of alleles → low diversity.
Mention that large populations avoid drift and maintain alleles through random mating.

Common mistakes

Confusing genetic drift with natural selection. Failing to explain that the bottleneck reduced allele numbers, not just individuals. Using vague terms like ‘different’ instead of ‘allelic variety’.

Mark scheme (4 marks)

The bottleneck event drastically reduced the number of individuals in the cheetah population
Only a small, non-representative sample of alleles from the original population survived the bottleneck
The subsequent cheetah population expanded from this genetically restricted founder group, so lacks allelic variety
Leopard populations remained large, maintaining a wide range of alleles through continued random mating across a large gene pool

Key terms in this question

genetic diversity