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Imprinting
A cellular epigenetic process in which certain genes within an organism's cells are "disabled" (e.g., via methylation) during the earliest stage(s) of the organism's development. For example, the embryo of a female mammal (which receives two copies of the X chromosome-- one from each parent) disables one of those copies, at random, in each of its cells, so the female becomes a genetic mixture of its two parents.
Loss of imprinting (LOI) can sometimes occur in an adult organism. For examples:
- in mice, LOI of the gene which codes for insulin-like
growth factor-2 (IGF-2) results in the intestine's
epithelial cells reverting to a less-developed state
and also development of significantly more intestinal
tumors.
- in humans, LOI of the gene which codes for IGF-2 is
correlated with development of colorectal
cancer.
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