title: Biology of the X chromosome.
abstract: The biology of the X chromosome is unique, as there are two Xs in females and only a single X in males, whereas the autosomes are present in duplicate in both sexes. The presence of only a single autosome, which can occur as a result of an error in meiotic segregation, is invariably an embryonic lethal event. Monosomy for the X chromosome is viable because of dosage compensation, a system found in all organisms with an X:Y form of sex determination, which brings about equality of expression of most X-linked genes in females and males. In mammals, the dosage compensation system involves silencing of most of the genes on one X chromosome; it is called X chromosome inactivation. In this review, we focus first on recent advances in our understanding of the molecular basis of the X inactivation mechanism. Then we consider an unusual feature of X inactivation, the mosaic nature of the female and subsequent exposure to somatic cell selection.
authors.affiliation: Departments of Medicine and Genetics, University of Washington, Seattle, Washington 98195-7360, USA. gartler@genetics.washington.edu
authors.forename: S M
authors.initials: SM
authors.lastname: Gartler
authors.forename: M A
authors.initials: MA
authors.lastname: Goldman
mesh_terms: D000818:Animals; D019976:Cloning, Organism; D004303:Dosage Compensation, Genetic; D005260:Female; D030342:Genetic Diseases, Inborn / Q000235:genetics; D008040:Genetic Linkage; D006801:Humans; D008297:Male; D009030:Mosaicism / Q000235:genetics; D014960:X Chromosome / Q000502:physiology*