DNA methylation

DNA methylation is an epigenetic modification where methyl groups are covalently added to DNA bases (most commonly cytosine in CpG dinucleotides in mammals). Methylation near gene promoters generally reduces transcription, while methylation in gene bodies or repetitive elements has context-dependent effects.

Key points:

• Essential for normal development, X‑chromosome inactivation and genomic imprinting.
• Sensitive to environmental inputs during development and ageing.
• Enzymes called DNA methyltransferases (DNMTs) write methyl marks; ten‑eleven translocation (TET) enzymes participate in demethylation.

See also: Epigenetics, Genomic imprinting.