A level Biology B · Edexcel 9BI0 · Topic 8B
Mutations
Key points
- A gene mutation is a change in the base sequence of DNA: substitution, insertion or deletion.
- Because the code is degenerate, a substitution may be silent (same amino acid); a missense mutation changes one amino acid; a nonsense mutation creates a stop codon.
- Insertions and deletions cause a frameshift, changing every codon after the mutation, usually with severe effects.
- Mutations occur randomly, mostly during DNA replication; mutagens (UV light, ionising radiation, some chemicals) increase the rate.
- Chromosome mutations include non-disjunction, giving aneuploidy (e.g. trisomy 21) or polyploidy (common in plants).
- Mutations in genes controlling cell division (proto-oncogenes and tumour suppressor genes) can cause cancer.
Topic notesPremium
A mutation is a change in the DNA. Most are harmful or neutral, but mutations are the only source of brand-new alleles, so all genetic variation ultimately starts here.
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