molecular imprinting

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molecular imprinting The phenomenon in which there is differential expression of a gene depending on which parent it is inherited from. Genes are now thought to carry either a female or a male `imprint', which influences their expression in offspring. For example, the development of Huntington's disease in humans is delayed until midlife if the gene is inherited from the father (as occurs in the majority of cases), whereas inheritance from the mother causes the onset of symptoms early in childhood. Various other genetic disorders show a similar pattern of differential expression according to the source of the defective gene. One theory is that the genes are chemically `marked' in the germ cells with a characteristic male or female pattern of methylation, and that this methylation pattern influences their expression in the somatic cells of the offspring.