X-chromosome inactivation: molecular mechanisms and genetic consequences.

Mammalian X-chromosome inactivation results in dosage compensation for X-linked genes. More than 30 years after its discovery, the molecular bases of this inactivation are being revealed. Multiple mechanisms are responsible for the initiation of this developmental event and the maintenance of the inactive state. Somatic cellular mosaicism, which is the genetic consequence of X-chromosome inactivation, has a profound influence on the phenotype of mammalian females.