Transition (genetics)

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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).

Transition, in genetics and molecular biology, refers to a point mutation that changes a purine nucleotide to another purine (AG), or a pyrimidine nucleotide to another pyrimidine (CT). Approximately two out of three single nucleotide polymorphisms (SNPs) are transitions.[1]

Transitions can be caused by oxidative deamination and tautomerization.[2] Although there are twice as many possible transversions, transitions appear more often in genomes, possibly due to the molecular mechanisms that generate them.[3]

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.

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  1. ^ Collins DW, Jukes TH (April 1994). "Rates of transition and transversion in coding sequences since the human-rodent divergence". Genomics. 20 (3): 386–96. doi:10.1006/geno.1994.1192. PMID 8034311.
  2. ^ Mader, Sylvia S. (2016-09-26). Concepts of Biology (Just the facts 101). Cram101 Textbook Reviews. p. 79. ISBN 9781490290089.
  3. ^ Ebersberger I, Metzler D, Schwarz C, Pääbo S (June 2002). "Genomewide comparison of DNA sequences between humans and chimpanzees". Am. J. Hum. Genet. 70 (6): 1490–7. doi:10.1086/340787. PMC 379137. PMID 11992255.

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