Editing Genomic imprinting (section)

===Regulation===
The grouping of imprinted genes within clusters allows them to share common regulatory elements, such as [[non-coding RNA]]s and [[differentially methylated regions (DMRs)]]. When these regulatory elements control the imprinting of one or more genes, they are known as imprinting control regions (ICR). The expression of [[non-coding RNA]]s, such as [[antisense RNA|antisense Igf2r RNA]] (''Air'') on mouse chromosome 17 and [[KCNQ1OT1]] on human chromosome 11p15.5, have been shown to be essential for the imprinting of genes in their corresponding regions.<ref>{{cite journal | vauthors = Mancini-Dinardo D, Steele SJ, Levorse JM, Ingram RS, Tilghman SM | title = Elongation of the Kcnq1ot1 transcript is required for genomic imprinting of neighboring genes | journal = Genes & Development | volume = 20 | issue = 10 | pages = 1268–1282 | date = May 2006 | pmid = 16702402 | pmc = 1472902 | doi = 10.1101/gad.1416906 }}</ref>

Differentially methylated regions are generally segments of DNA rich in [[cytosine]] and [[guanine]] nucleotides, with the cytosine nucleotides methylated on one copy but not on the other. Contrary to expectation, methylation does not necessarily mean silencing; instead, the effect of methylation depends upon the default state of the region.<ref>{{cite journal | vauthors = Jin B, Li Y, Robertson KD | title = DNA methylation: superior or subordinate in the epigenetic hierarchy? | journal = Genes & Cancer | volume = 2 | issue = 6 | pages = 607–617 | date = June 2011 | pmid = 21941617 | pmc = 3174260 | doi = 10.1177/1947601910393957 }}</ref>