Describe the causes and types of outcome of mutations, and explain how mutations contribute to genetic variation within a species.

Edexcel GCSE Biology (1BI0) — 3.5 Variation and mutation · 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 the DNA base sequence.

The outcome of a mutation can be:
1. Beneficial – improves fitness.
2. Damaging – reduces fitness.
3. Neutral – no effect on fitness.

Mutations create new alleles. These new alleles can be transmitted through sexual reproduction, thereby increasing genetic variation within the species.

Examiner tips

Use the word "mutation" first, then define it as a random DNA change. List all three outcomes (beneficial, damaging, neutral) to get full marks. Explain that new alleles are produced and can be passed on, linking to increased variation.

Common mistakes

Failing to mention all three outcomes, or only giving two. Using vague terms like "change" instead of "mutation". Omitting the link between new alleles and increased genetic variation.

Mark scheme (4 marks)

A mutation is a random change in the base sequence of DNA
Mutations may be beneficial, damaging, or neutral (all three required for this mark, or any two for half credit — award 1 mark for all three outcomes correctly stated)
Mutations introduce new alleles (versions of a gene) into a population
These new alleles can be passed on during sexual reproduction, increasing genetic variation in phenotypes across the species

Key terms in this question

mutation · genetic variation