The genetic code is made up of ‘letters’ called bases. Every three bases makes up a ‘word’ called a codon which codes for an amino acid. So during translation, codons are read by cellular ‘machines’ to make a chain of amino acids (a polypeptide, later to become a protein).
A frameshift is a very radical type of mutation in that alters how the codons are read (i.e. it alters the reading frame). If a base is added to a gene, all codons thereafter will be changed. This is because the added base forces all following bases to move one place forward. So the end base of a codon will become the start base of another codon.
Frameshifts and Nylonase
Frameshifts can produce a number of stop codons, and especially so when the sequence of bases is long. This fact shows why the nylonase adaption in bacteria did not arise from a frameshift — the gene lacks stop codons in 1,535 bases.
- Yomo, T., Urabe, I. and Okada, H., No stop codons in the antisense strands of the genes for nylon oligomer degradation, Proceedings of the National Academy of Sciences USA89:3780–3784, 1992.