The genetic code is considered to be degenerate because a single amino acid may be coded for more than one codon. In this case, Leucine (Leu) is an amino acid that can be encoded by four different codons: CUU, CUC, CUA and CUG codons. In consequence, all nucleotide changes (mutations) at the third codon position don't affect the synthesis of Leu. This type of mutation that does not alter the sequence of amino acids is called silent mutation.
