Dictionary of Human Evolution and Biology

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X Inactivation

Normal inactivation of one of two randomly selected X chromosomes in each cell of a female mammal. X inactivation happens early in embryonic development (in humans, during the third week). It occurs randomly in mammalian embryonic cells destined to become the individual, but nonrandomly in other tissues of the conceptus.

See mosaicism, heteropycnosis, and Barr body. Aka random X inactivation.

Cf. paternal-X inactivation.

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