What is DNA methylation?
Methylation of cytosine is a covalent modification of DNA, in which the H5 of cytosine is replaced by a methyl group. In mammals, 60%-90% of all CpGs are methylated. Methylation adds information not encoded in the DNA sequence, but it does not interfere with the Watson-Crick pairing – the methyl group is positioned in the major groove of the DNA. The pattern of methylation controls protein binding to target sites on DNA, affecting changes in gene expression and in chromatin organization, often silencing genes, which physiologically orchestrates processes like differentiation, and pathologically leads to cancer [reference see publication below].