Genetic codes known to Biopython are the ones specified by NCBI, available at http://www.ncbi.nlm.nih.gov/Taxonomy/Utils/wprintgc.cgi As in the previous recipe, the Biopython tutorial is your main port of call and is available at http://biopython.org/DIST/docs/tutorial/Tutorial.html Be sure to also check the Biopython SeqIO page at http://biopython.org/wiki/SeqIO