DNA methylation | definition of DNA methylation by Medical dictionary
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The modification of a DNA base by the addition of a methyl group (CH3). DNA methylation of cytosines in particular regions of a gene can cause that gene's suppression.
DNA methylation The addition of a methyl group to the cytosine ring that occurs in DNA when it is replicated in a dividing cell. The process forms methyl cytosine and is catalysed by enzymes called DNA methyltransferases. In humans, the change occurs only to those cytosines that preceded guanines in the DNA sequence. Methyl cytosine has a strong tendency to deaminate to form thymidine, and if this mutation is not repaired it remains. It is the commonest kind of genetic variation (polymorphism) in human populations.