Encyclopedia of Systems Biology

2013 Edition
| Editors: Werner Dubitzky, Olaf Wolkenhauer, Kwang-Hyun Cho, Hiroki Yokota

X Chromosome Inactivation

  • Vani Brahmachari
  • Shruti Jain
Reference work entry
DOI: https://doi.org/10.1007/978-1-4419-9863-7_859



In mammals, including humans, females have two X chromosomes and males have a single X along with the Y chromosome. Most of the genes on the X chromosome are expressed in both males and females and are necessary for the normal development and functions of all the cells in the body. Therefore, to compensate for the difference in the number of copies of the genes on the X chromosomes between the two sexes, one of the X chromosomes in female mammals is inactivated. Thus, dosage compensation is brought about by random inactivation of one the two X chromosomes in each cell very early in development when the fertilized egg has around 200 cells. However, once the paternally or the maternally inherited X chromosome is inactivated in a cell at this stage, the same X chromosome will be inactivated in all the cells derived from this cell throughout development and in the adult. Thus, the random inactivation of the X chromosome is an...

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  1. Mank JE (2009) The W, X, Y and Z of sex chromosome-dosage compensation. Trends Genet 25:226–233PubMedCrossRefGoogle Scholar

Copyright information

© Springer Science+Business Media, LLC 2013

Authors and Affiliations

  1. 1.Dr. B. R. Ambedkar Center for Biomedical Research, University of DelhiDelhiIndia