Genomic imprinting is an epigenetic chromosomal modification in the gametes or zygotes that results in a non-random monoallelic expression of specific autosomal genes depending upon their parent of origin. A gene could be materanlly imprinted (only paternal copy expressed) or paternally imprinted (only maternal copy expressed). The exact mechanism of genomic imprinting is not clear. However, allele-specific methylation of CpG residues at the 5' end of imprinted genes is thought to be responsible for the maintenance of imprinting in somatic cells.
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