- Not to be confused with the evolutionary concept of a transitional fossil.
In genetics, a transition is a mutation changing a purine to another purine nucleotide (A <-> G) or a pyrimidine to another pyrimidine nucleotide (C <-> T). Approximately two out of every three single nucleotide polymorphisms (SNPs) are transitions. They can be caused by oxidative deamination and tautomerization.[1] 5-Methylcytosine is more prone to transition than unmethylated cytosine, due to spontaneous deamination.
