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Updated: Dec 15 2020

Type of DNA Mutations

  • Silent
    • Exchange of one base for another results in same amino acid
      • often an alteration in 3rd position of codon
        • tRNA wobble
    • No change in protein function
  • Missense
    • Exchange of one base for another results in changed amino acid
      • transversion → exchanges a purine to a pyrimidine or a pyrimidine to a purine
        • e.g., C → A or G → T
      • transition → exchanges a purine for another purine or a pyrimidine to another pyrimidine
        • e.g., A → G or C → T
    • Variable change in protein function
      • if the new amino acid is similar to old (leu → ile) the protein will most likely function the same
      • if the new amino acid is different (glu → val) the protein folding/stability will likely be affected
    • e.g., sickle-cell anemia
      • glu → val mutation in β-globin gene
  • Nonsense
    • Exchange of one base for another results in a stop codon
    • Loss of function mutation as peptide is truncated
  • Frameshift
    • Deletion or addition of 1 or 2 bases resulting in misreading of all nucleotides downstream
    • Loss of function mutation as peptide is completely different
  • Large Segment Deletion
    • Unequal crossover at meiosis results in loss of large segment of DNA
    • Loss of function mutation
    • e.g., α-thalassemia
      • deletion of α-globin gene
  • Change at splice site
    • Alteration in base sequence at mRNA splicing site results in altered splicing
      • can remove parts of exon
      • can leave parts of intron
    • Variable effect on protein function as number of spliced amino acids varies
    • e.g., β-thalassemia
  • Triplet repeat expansion
    • Expansion of short nucleotide sequence results in longer polypeptide
      • can be in coding or noncoding region
    • Addition of amino acids affects protein structure/folding and affects function
    • Disease display anticipation
      • earlier disease onset in successive generations
    • e.g., myotonic dystrophy, Huntington's disease, and Fragile X
  • In-frame
    • In-frame mutations
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