Epigenetic processes, including DNA methylation, histone modifications, and non-coding RNA expression, act coordinately to regulate cellular differentiation and homeostasis. During development, different cell types acquire distinct DNA methylation profiles that reflect their developmental stage and functional identity. For most genes, the pattern of DNA methylation is identical on both alleles; at more evolutionarily complex loci, including imprinted and X chromosome genes, however, only a single allele is normally methylated.
