Each sense codon specifies one and only one amino acid.
Though redundancy in the genetic code certainly exists, with each amino acid in some cases specified by more than one codon, each codon nonetheless specifies only one amino acid. Exceptions are when a codon is a stop codon and therefore does not specify any amino acid (that is, some codons do not specify one amino acid because they do not specify any amino acids).See also lack of punctuation between codons.
Serving double duty, but nevertheless not displaying ambiguity, is the start codon, which not only serves to initiation translation but specifies the amino acid methionine. Nonetheless, within reading frames AUG still consistently specifies methionine so is not ambiguous in its specificity.
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