A point mutation is a mutation that only affects a single nucleotide of nucleic acid. Point mutations most commonly involve the substitution of one base for another (which changes the complementary base as well in DNA). The term point mutationt also includes insertions or deletions of a single base pair. Point mutations rarely cause a huge change in the underlying organism, which is fortunate as they are by far the most common type of mutation.
Single base substitutions can be divided into transitions and transversions based on whether or not they change the nucleobase's structure. Transitions, which change a nucleotide from a purine to purine or pyrimidine to pyrimidine, occur far more often than transversions, especially within coding regions of the genome.
When a point mutation does occur in a coding region, it can be assigned to one
of the following categories, according to the consequence of the mutation (see the figure below
for an illustration of different mutations applied to