Nonsynonymous Substitution (Molecular Biology)

Nonsynonymous substitution is an evolutionary term meaning the fixation in a population or subpopulation of a missense mutation, ie, a mutation that changes a codon into another codon that specifies a different amino acid. Nonsynonymous substitutions can be conservative, ie not greatly alter the function of the altered protein (see Conservative Substitutions). Nonsynonymous substitutions that are not conservative may indicate an adaptive change in the altered protein. This can only be confirmed, however, by demonstrating that the substitution changes the function of the protein.