Definition: 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 (copy from the father) that is inactivated.
Source: National Human Genome Research Institute's Talking Glossary of Genetic Terms
Synonyms:
  • Lyonization
  • X-inactivation