(Science: molecular biology) process by which methyl groups are added to certain nucleotides in genomic dna.
this affects gene Expression, as methylated dna is not easily transcribed. The degree of methylation is passed on to daughter strands at mitosis by maintainance dna methylases. Accordingly, dna methylation is thought to play an important developmental role in sequentially restricting the transcribable genes available to distinct cell lineages.
in bacteria, methylation plays an important role in the restriction systems, as restriction enzymes cannot cut sequences with certain specific methylations.