Edexcel IGCSE Double Science: Biology

Revision Notes

3.2.6 Mutation

Mutations

  • Mutations are rare, random changes that occur in the sequence of DNA bases in a gene or a chromosome
  • Mutations occur continuously
  • As the DNA base sequence determines the sequence of amino acids that make up a protein, mutations in a gene can sometimes lead to a change in the protein that the gene codes for
  • Most mutations do not alter the protein or only alter it slightly so that its appearance or function is not changed
  • There are different ways that a mutation in the DNA base sequence can occur

Insertions

  • A new base is randomly inserted into the DNA sequence
  • An insertion mutation changes the amino acid that would have been coded for by the group of three bases in which the mutation occurs
    • Remember – every group of three bases in a DNA sequence codes for an amino acid
  • An insertion mutation also has a knock-on effect by changing the groups of three bases further on in the DNA sequence

Insertion mutation, downloadable IGCSE & GCSE Biology revision notes

An example of an insertion mutation

Deletions

  • A base is randomly deleted from the DNA sequence
  • Like an insertion mutation, a deletion mutation changes the amino acid that would have been coded for by the group of three bases in which the mutation occurs
  • Like an insertion mutation, a deletion mutation also has a knock-on effect by changing the groups of three bases further on in the DNA sequence

Substitutions

  • A base in the DNA sequence is randomly swapped for a different base
  • Unlike an insertion or deletion mutation, a substitution mutation will only change the amino acid for the group of three bases in which the mutation occurs; it will not have a knock-on effect

Substitution mutation, downloadable IGCSE & GCSE Biology revision notes

An example of a substitution mutation

Author:

Alistair graduated from Oxford University in 2014 with a degree in Biological Sciences. He has taught GCSE/IGCSE Biology, as well as Biology and Environmental Systems & Societies for the International Baccalaureate Diploma Programme. While teaching in Oxford, Alistair completed his MA Education as Head of Department for Environmental Systems and Societies.
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