mutations

Sometimes, mutations cause a completely different amino acid to be put in
during translation. Mutations that actually alter the code are called missense
mutations. A nonsense mutation occurs when a message to stop translation
(called a stop codon) is introduced into the middle of the sequence (see
Chapter 9 for more on translation). The introduction of the stop codon
usually means the gene stops functioning altogether.
Mutations are often divided into two types:
 Neutral: When the amino acid produced from the mutated gene still creates
a fully functional, normal protein