Gene mutation

• What is a gene mutation?

  A change in the base sequence of DNA

  (This might lead to a change in the amino acid sequence of the encoded polypeptide)
• Most gene mutations occur spontaneously during DNA replication
• Why do gene mutations occur spontaneously during DNA replication?

  The rate of gene mutation is increased by exposure to mutagenic agents eg

  • UV radiation
  • ionising radiation
  • Chemical carcinogens
• What are the 6 types of gene mutation?

  • Substitution
  • Addition
  • Deletion
  • Inversion
  • Duplication
  • Translocation
• What is Substitution?


  One or more bases are swapped for another. May not lead to a change in amino acid sequence (due to degenerate code)
• What is addition?


  One or more bases added
• What is deletion?


  One or more bases are removed
• What is a frame shift?

  All triplets change downstream of/after the mutation (usually an added/deleted base)

  So all encoded amino acids also change (after the mutation)
• What is inversion?


  A sequence of bases is reversed
• What is duplication?


  One or more bases are repeated
• What is translocation?


  A sequence of bases is moved from one location in the genome to another (in the chromosome or another homologous chromosome)
• Practice Q.

  
• Importance of primary structure in encoded polypeptides