The effect of deletion mutations in codes without and with commas. (a) In a code without commas, a single-nucleotide deletion (here, deletion of a G residue) throws off the reading frame by one nucleotide. All amino acids added after this point are different from those in the wild-type protein. (b) In a code with commas separating the codons, the deletion should have minimal impact on the protein product because the next comma encountered after the deleted nucleotide would reset the ribosome to the correct reading frame. The genetic code of all living systems is now known to be without commas.