X‐chromosome Inactivation


X‐chromosome inactivation is an epigenetic process that silences the majority of genes on one of the two X‐chromosomes in female mammals. This silencing effectively equalizes dosage of X‐linked genes in females with that of males, who only possess one X‐chromosome and a sex‐determining Y‐chromosome.

Keywords: dosage compensation; epigenetics; chromatin modification; deoxyribonucleic acid methylation; sex chromosomes; transcriptional regulation

Figure 1.

In female cells one X‐chromosome is inherited from each parent. Random inactivation means that in some cells the paternally inherited X‐chromosome is inactivated, while in other cells the maternal X is inactivated. Cell proliferation and migration continue after inactivation and results in clumps of cells with either the paternal or maternal X inactivated. When the X‐chromosomes have different alleles this is apparent as clumps of cells with a different phenotype, such as the coat pattern in tortoiseshell cats.



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Further Reading

Avner P and Heard E (2001) X‐chromosome inactivation: counting, choice and initiation. Nature Reviews Genetics 2: 59–67.

Heard E, Clerc P and Avner P (1997) X‐chromosome inactivation in mammals. Annual Review of Genetics 31: 571–610.

Ng K, Pullirsch D, Leeb M and Wutz A (2007) Xist and the order of silencing. EMBO Reports 8: 34–39.

Web Links

X(inactive)‐specific transcript, antisense (TSIX); MIM number: 300181. OMIM: http://www.ncbi.nlm.nih.gov/entrez/dispomim.cgi?id=300181

X(inactive)‐specific transcript (XIST); MIM number: 314670. OMIM: http://www.ncbi.nlm.nih.gov/entrez/dispomim.cgi?id=314670

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Hore, Timothy A, Wakefield, Matthew J, and Graves, Jennifer AM(Apr 2008) X‐chromosome Inactivation. In: eLS. John Wiley & Sons Ltd, Chichester. http://www.els.net [doi: 10.1002/9780470015902.a0005795.pub2]