For at tage et eksempel, producerer cytosinmethylering [[5-Methylcytosin|5-methylcytosin]], som er vigtigt for [[Lyons hypotese|X-kromosominaktivering]].<ref>{{cite journal | author = Klose RJ, Bird AP | title = Genomic DNA methylation: the mark and its mediators | journal = Trends Biochem Sci | volume = 31 | issue = 2 | pages = 89–97 | year = 2006 | pmid = 16403636 | doi = 10.1016/j.tibs.2005.12.008 }}</ref> Det gennemsnitlige methyleringsniveau varierer mellem organismer&nbsp;– ormen ''[[Caenorhabditis elegans]]'' har ingen cytosinmethylering, mens [[hvirveldyr]] har højere niveauer, med 5-methylcytosin i op til 1% af deres DNA .<ref>{{cite journal | author = Bird A | title = DNA methylation patterns and epigenetic memory | journal = Genes Dev | volume = 16 | issue = 1 | pages = 6–21 | year = 2002 | pmid = 11782440 | doi = 10.1101/gad.947102 }}</ref> På trods af 5-methylcytosins vigtighed har det den ulempe, at det kan [[deaminering|deamineres]] til en thyminbase, hvilket gør methylerede cytosiner særligt sårbare over for [[mutation]]er.<ref>{{cite journal | author = Walsh CP, Xu GL | title = Cytosine methylation and DNA repair | journal = Curr Top Microbiol Immunol | volume = 301 | pages = 283–315 | year = 2006 | pmid = 16570853 | doi = 10.1007/3-540-31390-7_11 | isbn = 3-540-29114-8 | series = Current Topics in Microbiology and Immunology }}</ref> Blandt andre basemodifikationer er adeninmethylering i bakterier, tilstedeværelsen af [[5-hydroxymethylcytosin]] i [[hjerne]]n<ref>{{cite journal | author = Kriaucionis S, Heintz N | title = The nuclear DNA base 5-hydroxymethylcytosine is present in Purkinje neurons and the brain | journal = Science | volume = 324 | issue = 5929 | pages = 929–30 | year = 2009 | pmid = 19372393 | pmc = 3263819 | doi = 10.1126/science.1169786 | bibcode = 2009Sci...324..929K }}</ref> og [[glykosylering]]en af uracil til "J-basen" i [[kinetoplastider]].<ref>{{cite journal | author = Ratel D, Ravanat JL, Berger F, Wion D | title = N6-methyladenine: the other methylated base of DNA | journal = BioEssays | volume = 28 | issue = 3 | pages = 309–15 | year = 2006 | pmid = 16479578 | pmc = 2754416 | doi = 10.1002/bies.20342 }}</ref><ref>{{cite journal | author = Gommers-Ampt JH, Van Leeuwen F, de Beer AL, Vliegenthart JF, Dizdaroglu M, Kowalak JA, Crain PF, Borst P | title = beta-D-glucosyl-hydroxymethyluracil: a novel modified base present in the DNA of the parasitic protozoan T. brucei | journal = Cell | volume = 75 | issue = 6 | pages = 1129–36 | year = 1993 | pmid = 8261512 | doi = 10.1016/0092-8674(93)90322-H }}</ref>
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