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. Author manuscript; available in PMC: 2013 Nov 24.
Published in final edited form as: Semin Reprod Med. 2012 Apr 27;30(2):10.1055/s-0032-1307417. doi: 10.1055/s-0032-1307417

Figure 2.

Figure 2

Expression of imprinted and nonimprinted genes. According to classical genetics, genes are expressed from either both alleles (gene A) or none of them (gene B). This is true for most of the genes that are not imprinted. However, a subset of genes are imprinted; that is, their imprinting control regions are methylated on either the maternal or paternal allele allowing expression of only the paternal allele (gene C) or the maternal allele (gene D), respectively. This sex-specific parent-of-origin allelic methylation mark is inherited from one generation to another. Nonexpressed genes are indicated by red boxes with blunt arrows; expressed genes are depicted with green boxes with an arrowhead.