Python Programming for Biology: Bioinformatics and Beyond

Figure 14.2.  How changes in a protein sequence depend on codons. When DNA

sequences that correspond to the protein-coding region of a gene are aligned we can

observe mismatches that arise from nucleotide substitutions. However, in order to

determine what effect, if any, there will be in the protein sequence we must consider what

the differences are in the three-letter codons. Because an amino acid is usually encoded by

more than one three-letter codon a nucleotide change may have no effect; the change can

be synonymous. Whether there is a difference will depend on the genetic code and the

precise codon change.