To ensure that women and men express equivalent levels of the genes found on X chromosomes, one of the two X chromosomes in the cells of a women is inactive. X chromosome inactivation (XCI) occurs early in development, at approximately the time an embryo implants in the womb, and all cells stemming from a given cell have the same X chromosome inactivated.
Which X chromosome is inactivated is random and most females have approximately equal numbers of cells with each X chromosome inactivated. However, some individuals have a much greater proportion of their cells with a given X chromosome inactivated.
Such skewing of XCI can have clinical implications, for example, increased XCI skewing has been linked to premature ovarian failure and recurrent spontaneous abortion. To use XCI skewing effectively as a clinical tool more information is needed about the underlying mechanisms.
In a new study, Lambert Busque and colleagues at the University of Montreal, have shown that XCI skewing is a complex trait determined by secondary events and selection biases rather than being the result of an inherited tendency to inactivate a particular X chromosome.
Carolyn Brown and colleagues from the University of British Columbia, Vancouver, highlight the importance of these observations in an accompanying commentary.
Article: No evidence that skewing of X chromosome inactivation patterns is transmitted to offspring in humans. Journal of Clinical Investigation. December 20, 2007.
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