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SystemFantastic1090 t1_j99fzu1 wrote

It’s a myth that every single gene on the X chromosome is silenced during X-linked inactivation. In reality, many escape inactivation and are still expressed. It’s the lack of these that cause many (if not all) of the problems in Turner’s syndrome.

If you want to read up more on which escape X-inactivation, search “four core genotype” model and go from there

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PoiseandPotions t1_j9geib8 wrote

Replying to SystemFantastic1090 (#1,881,031)

Piggybacking off of this, it’s 100% right that just because one X is turned into a Barr Body doesn’t mean it doesn’t have any activity. There are still parts of the ‘inactivated’ X that are expressed. For context, just look at how much smaller the Y chromosome is than the X one. Not to stir up a battle of the sexes, but a typical X chromosome is ~5x as big as a Y chromosome. So even a mostly inactivated X still has some activity equivalent to a Y chromosome.

Also, which X gets turned into a Barr Body is a random process (at least in humans), so in some cells it’s the maternal X that’s turned into a Barr Body, and in other cells it’s the paternal one. This is why we still see traits from both parents, and still use both X’s.

As for the infertility issue, from what we can tell, the parts of the Barr Bodies that we do use are mostly linked to creating the growth hormones and sex hormones that are responsible for attaining adult height and development of secondary sex characteristics. They also help reproductive organs develop naturally. It’s not uncommon for a person with turners syndrome to have ‘smear gonads’ or ‘smear ovaries’ that are essentially just a cluster of cells that are trying to be an ovary but just aren’t quite fully formed. This understandably leads to infertility because the ovaries don’t develop, and can be at a much higher risk of cancer as a result.

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