Transition (genetics)

Transition, in genetics and molecular biology, refers to a point mutation that changes a purine nucleotide to another purine (A ↔ G), or a pyrimidine nucleotide to another pyrimidine (C ↔ T).

Approximately two out of three single nucleotide polymorphisms (SNPs) are transitions.

[3] Transitions are more likely to be synonymous substitutions than transversions, as one observes in the codon table.

5-Methylcytosine is more prone to transition than unmethylated cytosine, due to spontaneous deamination.

This mechanism is important because it dictates the rarity of CpG islands.

Illustration of a transition: each of the 4 nucleotide changes between purines or between pyrimidines (in blue). The 8 other changes are transversions (in red).