7.5 Genetic Mutations

Small - Scale Mutations

• Point mutations - change in individual base pair, or small groups
  • Substitution
  • Insertion / Deletion
  • Inversion
• Effects: amplified by # of codons affected
  • Missense
  • change in amino acid sequence
  • Nonsense
  • results in premature stop codon
  • polypeptide is shorter
  • Silent
  • no change in amino acid sequence
  • Frameshift
  • reading frame is changed resulting in different amino acid sequence from point of mutation

Large - Scale Mutations

• Multiple nucleotides, entire genes, or multiple genes
• Types or large-scale mutations
  • Amplification / Gene Duplication: additional copies of genes
  • Deletion: loss of entire genes
  • deletion of dystrophin gene results in Duchenne muscular dystrophy
  • Translocation: movement of entire genes to another region of same or other chromosome
  • may disrupt gene at point of insertion or result in a new polypeptide
  • Inversion: region in a gene reverses direction

Causes of Genetic Mutation

• Spontaneous
  • caused by error in replication
• Induced
  • caused by a mutagen (an environmental agent that can alter DNA sequence)
  • Chemical mutagens:
  • some mutagens modify nucleotides to resemble others, this leads to inaccurate copying because incorrect base pairs are inserted
  • others cause mutation because they have similar structures to a nitrogenous base and are mistakenly inserted, disrupting DNA structure (ex: ethidium bromide)
  • Radiation:
  • low energy radiation can affect the structure of the DNA molecule leading to complication in replication and transcription
  • high energy radiation (ionizing radiation) can break bonds and cause large-scale mutations