A nucleotide change is synonymous if it does not cause the codon to code for a different amino acid. A nucleotide site in which one or more changes is synonymous is referred to as a synonymous site. If only one of three possible nucleotide changes at that site is synonymous, then the site is 1/3 synonymous. If two of three nucleotide changes are synonymous, then the site is 2/3 synonymous and 1/3 nonsynonymous. And, if all three possible nucleotide changes are synonymous, then the site is completely synonymous.