AGB 121: Principles of Animal Genetics and Population Genetics (2+1)

SILENT MUTATION

• Any gene mutation which does not result in phenotypic expression is called a Silent Mutation.
• Silent mutations are of several types.
  • The genetic code is degenerate, (most amino acids are coded for by several alternative codons)
    • Mutation may occur in the third location of the codon, the resulting new codon may still code for the same amino acid.
    • For example both AAG and AAA specify lysine. If the codon AAG undergoes a mutation to AAA the latter codon will still specify lysine. When a mutated triplet codes for the same amino acid, results in no effect on the amino acid sequence of the gene product.
  • The codon change may result in an amino acid substitution, but this amino acid change may not modify the activity of the protein.
  • The mutation may occur in a gene that is no longer functional or whose protein is not essential at the particular stage of testing.
  • Simultaneous presence of suppressor mutations may cause a mutation to become silent. In genetic suppression a second mutation at a different site neutralizes the effects of the first mutation.