The phenomenon in a female by which one X chromosome (either the maternally or paternally derived X) is randomly (by chance) inactivated in an early embryonic cell, with fixed inactivation of that same X in all cells descended from that cell. The change that occurs with X inactivation is epigenetic: it is a heritable change in gene function without [..]

The process and result of one of a pair of X chromosomes becoming silent or inactive in a female mammal; typically occurs in early embryonic development and affects the life of the female. © N [..]

The condensation of all but one of the X chromosomes of a mammal into a heterochromatic state, eliminating gene expression from all but the active X chromosome. This process ensures that male and female mammals have the same level of gene activity of X-chromosome genes.