- 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: GeneReviews
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 Terms from the National Human Genome Research Institute
See also Understanding Medical Terminology.