= Frameshift mutation
{wiki}
A <frameshift mutation> changes downstream grouping into <codons> through insertion or deletion of a number of <nucleotides> not divisible by three. In the constructed <messenger RNA> example, insert C immediately after AUG while retaining the same initiation position: $\mathrm{AUG\;CGC\;UUU\;CUG}\;(\mathrm{A})$. The first <codon> is preserved, but the original downstream groups GCU, UUC and UGA disappear. The displayed fragment now has no complete standard <stop codon>; what happens later depends on its continuation.
The short proof is positional: every downstream <nucleotide> moves by $k$ positions after an insertion of length $k$. Boundaries recur every three positions, so they retain the original phase exactly when $k$ is divisible by three. An insertion of three <nucleotides> can still change the <peptide>, but it does not shift the downstream <reading frame>. This distinction helps interpret <genetic variants> without predicting a particular <phenotype> from grouping alone.<Biology 2e by Mary Ann Clark and others>[§15.1, The Genetic Code, Figure 15.5: nucleotide deletion and shifted grouping]{ref}
Back to article page
