Describe how a mutation can lead to extinction of a species if natural selection occurs too slowly.

WJEC GCSE Biology (Wales) — 2.4.2 Evolution and natural selection · Describe · 4 marks · View as Markdown

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

A small population of beetles lives in a forest. Over time, the temperature of the forest environment rises significantly. A mutation occurs in some individuals that affects their ability to regulate body temperature.

Model answer (4 marks)

A mutation is a random change in DNA that increases variation.
If the mutation does not produce an advantageous phenotype, the organisms are not well suited to the new environmental conditions.
Individuals without a beneficial allele are less likely to survive and reproduce, so fewer advantageous alleles are passed to offspring.
If natural selection is too slow, the whole species dies out before it can adapt, leading to extinction.

Examiner tips

Use the exact terms: mutation, variation, advantageous phenotype, survival and reproduction, natural selection, extinction.
Show the causal chain: mutation → variation → selection pressure → survival/reproduction → allele frequency → extinction if selection is slow.

Common mistakes

Confusing mutation with natural selection; describing mutation as beneficial when it may be neutral or harmful.
Failing to link the lack of advantageous phenotype to reduced survival and reproduction.
Not mentioning that extinction occurs because the species cannot adapt in time.

Mark scheme (4 marks)

A mutation is a random change in DNA / which increases variation
If the mutation does not produce an advantageous phenotype / the organisms are not well suited to the new environmental conditions
Individuals without a beneficial allele are less likely to survive and reproduce / fewer advantageous alleles are passed to offspring
If natural selection is too slow, the whole species dies out before it can adapt / this leads to extinction

Key terms in this question

mutation · natural selection · extinction