The rules that determine which triplet of nucleotides code for which amino acid during translation. There are more than 20 different amino acids and four bases (adenine, thymine, cytosine and guanine). There are 64 potential combinations of the four bases in triplets (4 × 4 × 4). A doublet code would only be able to code for 16 (4 × 4) amino acids. Since only 20 amino acids exist, there is redundancy in the system so that some amino acids are coded for by two or more different triplets (codons).