Genomic Imprinting:Parental differentiation of the genome

Genomic imprinting is the biological process whereby a gene or genomic domain exists in a state of epigenetic differentiation that depends upon its parent of origin. Importantly, the establishment and propagation of these parent-specific genomic conformations does not alter the primary DNA sequence comprised of A, C, G, and T nucleotides. Genomic imprints may be covalent (DNA methylation) or non-covalent (DNA-protein and DNA-RNA interactions, genomic localization in nuclear space), and the process of imprinting encompasses the specialized nuclear enzymatic machinery that maintains parental epigenetic markings throughout the cell cycle. Because of genomic imprinting, the parent of origin of homologous genetic alleles in diploid individuals can be determined in the absence of DNA sequence polymorphisms and without recourse to parental DNA samples. As illustrated in Figure 1, alleles of imprinted genes look and behave differently, as determined by parent of origin.