noun, plural: missense mutations
Mutation is a change in the nucleotide sequence of a gene or a chromosome. When there is only one nucleotide involved, it is particularly referred to as a point mutation. Point mutation occurring in noncoding sequences often does not result in an altered amino acid sequence during translation. However, if a mutation in the promoter sequence of a gene occurs, the effect may be apparent since the expression of the gene may cause changes in the amino acid sequence, as well as the structure and function of the protein product. Point mutations may be classified based on functionality: (1) nonsense mutation, (2) missense mutation, and (3) silent mutation.
A missense mutation may lead to the synthesis of a protein that is nonfunctional. For instance in sickle-cell disease, the 20th nucleotide of the gene for the beta chain of hemoglobin on chromosome 11 is changed from the codon GAG to GTG so that when translated the 6th amino acid is now a valine instead of glutamic acid.