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[olaf.larsson]

I have a question about the so called Barr body in females. X-linked recessive deseases are very uncommon in females. So how could one of the X-es be said to be constitute the "inactivate" Barr body. If one X was really inactive there would be no advantage for females to have two X-es instead of one when considering diseases like hemophilia etc. So how could one of the X be considered inactive, yet contribute to production of functional proteins??? [:o]

[olaf.larsson]

Well I have found the info myself. It turns out that womens are actually a mosaic of diffrent X-chromosomes active in diffrent cells, a fact that I was not aware of:

http://en.wikipedia.org/wiki/Barr_body

This means that monozygotic female twin are more phenotypicly diffrent from each other than male monozygotic twins since female monozygotes differ in the pattern of X-inactivation.