noun, plural: substitution mutations
Mutation is a change in the nucleotide sequence of a gene or a chromosome. Based on the effect of mutation on the gene structure, mutations may be: (1) small-scale mutations or (2) large scale mutations. Small-scale mutations are a type of mutation where one or few nucleotides of a gene are affected. They are further classified as follows: (1) substitution mutations, (2) insertion mutations, and (3) deletion mutations.
Substitution mutations are a type of mutation in which a single nucleotide is substituted with a different nucleotide. Examples of (base-pair) substitutions: a purine is substituted with a different purine (A → G) or a [[pyrimidine],] for a different pyrimidine (C → T). This type of substitution mutation is referred to as transition. Another type of base-pair substitution is the so-called transversion. In transversion, a purine is substituted with a pyrimidine or a pyrimidine with a purine.