Skip Navigation
Genetics Home Reference: your guide to understanding genetic conditions About   Site Map   Contact Us
 
Home A service of the U.S. National Library of Medicine®
A | B | C | D | E | F | G | H | I | J | K | L | M | N | O | P | Q-R | S | T | U | V | W | X | Y-Z

X-chromosome inactivation

Synonym(s)

  • lyonization
  • X-inactivation

Definition(s)

In females, the phenomenon by which one X chromosome (either maternally or paternally derived) is randomly inactivated in early embryonic cells, with fixed inactivation in all descendant cells; first described by the geneticist Mary Lyon

Definition from: GeneReviewsThis link leads to a site outside Genetics Home Reference. from the University of Washington and the National Center for Biotechnology Information

Lyonization is commonly known as X-inactivation. In mammals, males receive one copy of the X chromosome while females receive two copies. To prevent female cells from having twice as many gene products from the X chromosomes as males, one copy of the X chromosome in each female cell is inactivated. In placental mammals, the choice of which X chromosome is inactivated is random, whereas in marsupials it is always the paternal copy that is inactivated.

Definition from: Talking Glossary of Genetic TermsThis link leads to a site outside Genetics Home Reference. from the National Human Genome Research Institute

See also Understanding Medical Terminology.

 
Published: July 7, 2014