Point mutations

Point mutations are those mutations that affect a single base pair. The most common nucleotide mutations are substitutions, in which one base is replaced by another. These can be of two types, either transitions or transversions. Transition substitution refers to a purine or pyrimidine being replaced by a base of the same kind; for example, a purine such as adenine may be replaced by the purine guanine. Transversion substitution refers to a purine being replaced by a pyrimidine, or vice versa; for example, cytosine, a pyrimidine, is replaced by adenine, a purine.

Depending on the change in the coding sequence the point mutations can be categorized into following three groups:

Silent mutations have no effect on the protein sequence. Missense mutations result in an amino acid substituation. Nonsense mutations lead to the substitution with a stop codon.