DNA methylation involves adding methyl groups to CpG dinucleotides, often clustered in gene promoter regions called CpG islands. This modification leads to gene silencing by a few mechanisms: - Methyl groups physically impede the binding of transcription factors required to initiate mRNA synthesis. - Methylated DNA recruits proteins like MeCP2 that further repress transcription through chromatin remodeling. - Heavily methylated genes accumulate repressive histone marks over time that stably lock in the silent state.