The differential expression of a gene according to whether it is derived from the mother or father. This leads to unequal genetic contributions from the mother and father to their offspring and is essential for normal development. For example, loss of maternal imprinting in mice results in an abnormally large fetus, whereas loss of paternal imprinting leads to a small fetus. Several human diseases are associated with failures of imprinting, including Angelman syndrome and Prader-Willi syndrome. A diverse range of organisms, including plants, insects, and mammals, exhibit gene imprinting. It depends on the methylation of certain bases, particularly cytosine residues, in the DNA, effectively silencing expression of the affected gene, possibly by causing inhibitory proteins to bind to methylated residues. Another imprinting mechanism is evident in yeast, fruit flies, and the nematode Caenorhabditis elegans. Here, imprinting is determined by patterns of chemical modifications of the histone proteins that package the DNA into chromatin (see chromatin silencing). Such patterns, although reversible, are inherited by being incorporated as the DNA is replicated.
Subjects: Biological Sciences.