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marieterna t1_ivxtpw0 wrote

I believe ~10-15% of genes on the Barr Body escape X-inactivation. This means that in the X0 genotype, you are missing those 10-15% genes and their expression, which is an issue. It’s the opposite in Klinefelter’s, XXY genotype. Because you have two X chromosomes, one undergoes X-inactivation which is to be expected in the XX genotype. But you have 10-15% MORE due to that Barr Body, since in a normal XY genotype, you’re not supposed to have that extra X.

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Cultural-Opposite937 t1_ivya4b2 wrote

This is correct, the region that isn't inactivated is called the psudoautosomal region and is what allows the pairing between the X and Y (or two Xs) during meiosis.

People with only 1 X have haploinsufficnacy for the genes in this region and that leads to the alteration in their phenotype, including non-functioning ovaries or streak gonads (phenotype can vary).

Those with trisomy of the sex chromosomes (XXX, XXY, XYY) may also have altered phenotype due to overdosing of the genomic products of these regions (though XXY tends to have more effect than XXX and XYY doesn't seem to have much effect at all, despite what early studies may claim). Instances of these are also much higher than Turners syndrome (1 in 500 for XXX and 1 in 1000 for XXY and XYY)

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