missense mutation

A missense mutation is a substitution that changes a codon so that it now specifies a different amino acid. It is like a typo that turns one valid word into another valid but wrong word — the sentence still reads, but its meaning has shifted at that spot.

Because the protein is built from a chain of amino acids, swapping one for another may or may not matter. If the new amino acid is chemically similar and sits in an unimportant part of the protein, the change is often tolerated, sometimes called conservative. If it sits at the active site or disrupts folding, the protein's function can be impaired or lost.

Missense mutations are responsible for many inherited conditions and are also a major source of harmless natural variation between individuals. Their effects are studied closely in medical genetics, where predicting whether a given amino acid change is benign or damaging remains a hard and important problem.