Because X-inactivation is random, in normal females the X chromosome inherited from the mother is active in some cells, and the X chromosome inherited from the father is active in other cells. Some genes on the X chromosome escape X-inactivation.

Is X inactivation random in each cell?

It is understood that X-chromosome inactivation is a random process, occurring at about the time of gastrulation in the epiblast (cells that will give rise to the embryo). The maternal and paternal X chromosomes have an equal probability of inactivation.

Is skewed X inactivation random?

The Xist gene is responsible for inactivating the X chromosome from which it is transcribed. X-chromosome inactivation in general is influenced by the number of guanine-containing nucleotides on the Xist promoter, although generally inactivation still follows a random pattern.