Any gene mutation which does not result in phenotypic expression is called a silent mutation.
Silent mutations are of several types.
1.The genetic code is degenerate, i.e. more than one codon may specify an 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 as the original there is no change in the amino acid.
This mutation is of the silent type, because although there is a change in the base sequence of DNA there is no alteration in the amino acid sequence of the protein synthesized.
2.
The
codon
change
may
result
in
an
amino
acid
substitution,
but
this
is
not
sufficient
to
modify
the
function
of
the
protein
appreciably
3. The mutation may occur in a gene that is no longer functional or whose protein is not essential at the particular stage of testing.
4. 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.
