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hypoE
12-28-2015, 12:13 AM
Hello All,

I discovered by accident recently that most likely my active x chromosome is actually from my father's maternal heritage.

1. I was wondering how common it is that the active x gene is from the opposite sex parent.
2. Are there implications about the strength or weakness of the other parents x gene or is it just random chance?
3. Would two female siblings most likely have the same active x in this case?

Afshar
12-28-2015, 07:45 AM
It is a completely random process (with the data we have now), but there are some papers about mice which hint a paternal preference for the X chromosome inactivation.
Interesting topic btw!

geebee
12-28-2015, 02:45 PM
In humans, there does not appear to be a preference for one X over the other. In addition, X inactivation takes places during embryonic development, and only applies to the given cell lines in which it occurs. In other words, a different X chromosome will be inactivated in different cells (and their descendants).

To illustrate this, let's consider the most common form of color blindness. In humans, there are three different photo pigments which are involved in our ability to see colors. The genes responsible for two of these are located on the X chromosome, and defects in either result in red-green color blindness/deficiency.

Because men only have a single X chromosome, if they inherit a chromosome with the defective gene(s), they will be affected. But if a woman inherits a chromosome with the defective gene, she should be affected roughly half the time. This is because if X-inactivation is random and is strictly a one-time thing for the entire body, then half the time it should be the X with the defective X chromosome that is the active one.

Instead, it turns out that women who are only carriers of a single X with the defective gene(s) almost always have normal color vision. Why? It is because at least some of the cone cells producing the affected color pigments are normal -- enough that a woman's color vision isn't noticeably compromised.