In all eutherian (mammals excluding the marsupials), the female (who is $XX$ for the pair of sexual chromosomes) inactivates one of her $X$. This is called dosage compensation. This inactivation occurs at a given time during the development when randomly one $X$ is silenced. The daughters of this cell inherit the $X$-inactivation pattern epigenetically, which results in some part of a tissue having the maternal $X$ inactivated while others having the paternal $X$ inactivated (daughters of some other cell which silenced the paternal $X$). This process yield to the famous turtoiseshell coat in female cats.


In short

Assuming X-inactivation occurred in the lineage of the oogonia/oocytes, when does the X-inactivation and X-reactivation occur in the lineage of the oocytes?

A bit developed

Are the X inactivated as well in primary oocytes? If not, is the $X$ inactivated in the secondary oocytes in a primary follicle? If not, did the diploid mother cells of the secondary oocytes have one $X$-inactivated? If yes, did all diploid mother cells of oocytes have the same $X$ inactivated (inactivation occurred relatively early in the development or is there an imprinting) or did the mother cells of oocytes differ in the $X$ they have inactivated (inactivation occurred relatively late in the development)

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    $\begingroup$ I'll post an elaborate answer in some time. Little occupied now $\endgroup$
    Aug 6, 2014 at 16:48

1 Answer 1


See these two papers:

Basically it happens just before the meiosis.


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