A gene mutation can change the base sequence of DNA. Explain how a gene mutation in a body cell could affect the protein produced by that gene, and why a mutation in a gamete is particularly significant for future generations.

Edexcel A-Level Biology A: Salters-Nuffield (9BN0) — 1.5 Gene mutations and genetic disorders · Explain · 5 marks · View as Markdown

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

Gene mutations are changes to the base sequence of DNA. They can occur spontaneously during DNA replication or be caused by mutagens such as ionising radiation or certain chemicals. Most mutations have no effect on the organism, but some alter the protein coded for by the gene.

Model answer (5 marks)

A mutation changes the order of bases in the DNA strand. The altered sequence is read by RNA polymerase and translated into a different sequence of amino acids. The new amino‑acid sequence changes the protein’s three‑dimensional shape, so it may lose its normal function or gain a new one. If the mutation occurs in a gamete, the altered gene is incorporated into the fertilised egg. All cells of the resulting embryo, and therefore all future generations, inherit the mutation, so it can be passed on to many descendants.

Examiner tips

  • Use the exact terms: base sequence, amino‑acid sequence, protein structure, gamete, offspring, all body cells
  • Show the chain: DNA → RNA → protein → function
  • Explain the significance of inheritance for future generations

Common mistakes

  • Saying the mutation only affects the cell where it occurs, ignoring inheritance
  • Using vague terms like ‘change’ instead of ‘altered base sequence’
  • Failing to mention that the mutation is present in every cell of the offspring

Mark scheme (5 marks)

  1. A gene mutation changes the base sequence / order of bases in the DNA
  2. The changed base sequence leads to a different sequence of amino acids being coded for
  3. A different amino acid sequence means the protein has a different shape / structure, so it may not function correctly
  4. A mutation in a gamete (egg or sperm) means the mutation is in the genetic material that is passed on to offspring
  5. Every cell of the offspring will contain the mutation / the mutation will be present in all body cells of the offspring, so all generations descended from that individual could inherit it

Key terms in this question

gene mutation · base sequence · gamete · protein

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