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X chromosome inactivation

Genetics as it applies to evolution, molecular biology, and medical aspects.

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X chromosome inactivation

Postby Nelsson » Wed Apr 23, 2008 12:56 pm

Hi! when a X chromosome inactivates in a female fetus, creating a Barr body, this happens independently and random. The random selection of which of the X chromosomes( maternal and paternal) to be inactivated in each cell, results in a female "mosaic", where the genes in the paternal X chromosome is expressed in some cells, and the maternal one i other cells.
What if this female person is heterozygot for a hereditary sex-linked disease on the X-chromosome, in what way does this affect the person? If approximately half of her cells express the allele causing the disorder and the other half expressing the "normal" allele, will she the be sick or not?
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Postby Darby » Wed Apr 23, 2008 8:21 pm

Most of those conditions are considered recessive for the reason you're asking about, but it's a system-wide response. Some cells express the disease, but not enough to affect the whole individual.
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Postby Cat » Mon Apr 28, 2008 1:41 am

The second X chromosome is not completely inactive. Don't forget about pseudoautosomal regions!
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Postby kk » Fri Mar 27, 2009 6:38 pm

X chromosome inactivation also occurs in males, in Klinefelter syndrome (XXY), but what happens if the individual has an extra Y chromosome (XYY)? Does one Y chromosome inactivate?
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Re: X chromosome inactivation

Postby casually » Sat Mar 28, 2009 5:23 pm

No. But too much y-encoded protein leads to symptoms like aggressiveness and slight mental retardation.
If there is too much x-chromosomes, all except of one will be inactivated. But due to incomplete inactivation there will always be symptoms.
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Postby MrMistery » Sun Mar 29, 2009 1:41 am

casually, that is a flawed view that was popular around the 60s and 70s. In current views, the only consequence of having an extra Y chromosome is that the individual is somewhat taller on average.
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