A nucleotide change is nonsynonymous if it changes the amino acid encoded by the original codon. A nucleotide site in which one or more changes are nonsynonymous is referred to as a nonsynonymous site. If only one of three possible nucleotide changes at that site is nonsynonymous, then the site is 1/3 nonsynonymous. If two of three nucleotide changes are nonsynonymous, then the site is 2/3 nonsynonymous. And, if all three possible nucleotide changes are nonsynonymous, then the site is completely nonsynonymous.