Describe how mutations contribute to variation within a population, and explain why most mutations have no effect on the phenotype of an organism.

AQA GCSE Biology (8461) — 4.6.2 Variation and evolution · Describe · 4 marks · View as Markdown

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

Model answer (4 marks)

A mutation is a random change in DNA.
Mutations may produce new alleles or genetic variants.
New alleles can lead to different phenotypes, increasing variation in the population.
Most mutations occur in non‑coding DNA or do not alter the amino‑acid sequence, so the protein remains unchanged and the phenotype is unaffected.

Examiner tips

  • Use the exact wording ‘random change in DNA’ and ‘new alleles’ to match the scheme.
  • Show the two parts: contribution to variation and why most are neutral.
  • Keep sentences concise and avoid extra explanation.

Mark scheme (4 marks)

  1. A mutation is a random change in DNA
  2. Mutations may produce new alleles / genetic variants
  3. New alleles can lead to different phenotypes / observable characteristics in the population, increasing variation
  4. Most mutations occur in non-coding DNA / the mutation does not change the sequence of amino acids / protein produced is unchanged

Key terms in this question

mutation · phenotype · variation

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