DNA methylation

• Chemical modification of cytosine to 5-methylcytosine (5mC) by the attachment of a methyl group to the fifth carbon atom of cytosine
• DNA methylation mainly occurs at CpG sites, i.e. cytosine nucleotides that are followed by a guanine nucleotide
• CpG sites are underrepresented in the genome since they are ‘mutational hotspots’: 5mC is prone to be deaminated to thymine, resulting in a C->T mutation

http://www.nature.com/milestones/geneexpression/milestones/articles/milegene10.html

http://www.nature.com/scitable/topicpage/The-Role-of-Methylation-in-Gene-Expression-1070

See also

MRE-seq