Mutations

• Mutations are changes in the DNA that can result in no protein or an altered protein being synthesized
• Single gene mutations:

  • Substitution: the replacement of one base, involving the alteration of a DNA nucleotide
  • Insertion: the addition of one base sequence as a result of substitution
  • Deletion: the removal of one base
• Substitution mutations, Insertion, and Deletion Mutations
• Effects of mutations on DNA sequence:

  • CGAcc6AcT -> CGAccGAC: one base added, one base change
  • L -> LL: one base change
  • CGAccGAA -> TCGACCC: three effects:
  • Missense: one amino acid is changed for another
  • Nonsense: premature stop codon, resulting in frame-shift mutations
  • Splice-site: introns may be retained or exons removed, causing a major effect on protein structure
• Chromosome Structure Mutations:

  • Translocation: non-homologous chromosomes alter the number or structure of chromosomes
  • Inversion: homologous chromosomes reverse their structure
  • Duplication: homologous chromosomes have a section added
  • Deletion: homologous chromosomes have a section removed
• Substantial changes in chromosome structure are often lethal

  • Deletion: a section of a chromosome is removed
  • Duplication: a section of a chromosome is added
  • Inversion: a section of a chromosome is reversed
  • Translocation: a section of a chromosome is added to a non-homologous chromosome, affecting genes like clotting factors and causing disorders like Haemophilia A or Cri-du-chat syndrome