Explain why the genetic diversity of a population is important for its long-term survival when environmental conditions change.

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).

A conservation charity is managing two isolated populations of a rare bird species. Population A consists of 400 individuals with a wide variety of alleles at many gene loci. Population B consists of 40 individuals, all descended from a single breeding pair introduced 20 years ago.

Model answer (4 marks)

Greater genetic diversity gives a wider range of phenotypes in the population.
Some individuals will carry alleles that are advantageous when conditions change.
Natural selection can then favour those individuals, allowing the population to adapt.
A population with little diversity may lack the necessary alleles, increasing the risk of extinction.

Examiner tips

Use the exact wording from the mark scheme – ‘greater genetic diversity’, ‘variation in phenotypes’, ‘natural selection’, ‘low genetic diversity’. Show the logical sequence: diversity → variation → selection → survival. Keep each point concise and separate them clearly.

Common mistakes

Using vague terms like ‘more genes’ instead of ‘greater genetic diversity’. Failing to link diversity to the ability to adapt or to extinction risk.

Mark scheme (4 marks)

Greater genetic diversity means more variation in phenotypes within the population
Some individuals are more likely to have alleles that are advantageous under the new conditions
Natural selection acts on this variation, so better-adapted individuals survive and reproduce
A population with low genetic diversity may lack suitable alleles, making extinction more likely

Key terms in this question

genetic diversity