Transition, ingenetics andmolecular biology, refers to apoint mutation that changes apurinenucleotide to another purine (A ↔G), or apyrimidine nucleotide to another pyrimidine (C ↔T). Approximately two out of threesingle nucleotide polymorphisms (SNPs) are transitions.[1]
Transitions can be caused byoxidative deamination andtautomerization. Although there are twice as many possibletransversions, transitions appear more often ingenomes,[2] possibly due to the molecular mechanisms that generate them.[3] Transitions are more likely to besynonymous substitutions than transversions, as one observes in thecodon table.
5-Methylcytosine is more prone to transition than unmethylatedcytosine, due to spontaneousdeamination. This mechanism is important because it dictates the rarity ofCpG islands.
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