Thread by @FondOfBeetles

@MargaretAtwood Why?

Microchimerism is common during/after pregnancy. It is the phenomenon that permits us to diagnose fetal sex and chromosome disorders from a maternal blood sample.

@MargaretAtwood If a female has carried a male child, those fetal cells she carries often incorporates will be XY.

Fetal microchimerism has outcomes for maternal health. Most wondrous is the role of fetal cells in tissue repair when pregnant Mum suffers tissue damage.

@MargaretAtwood Tracking fluorescent rat fetal cells when pregnant rat Mum has a cardiac arrest shows those fetal cells trafficking to the damaged tissue to contribute to repair.

Amazing stuff.

@MargaretAtwood The question really is: Why do you think microchimerism - the incorporation of fetal cells into Mum’s body - is relevant to that Mum’s sex category?

@MargaretAtwood The second example of ‘handwaving, oh so complicated’ is a male with PMDS. That is, a male who has successfully developed as male, but who has failed, for various genetic reasons, to successfully clear internal female precursors.

@MargaretAtwood That such males exist is not surprising. If we hadn’t ever found such a male, we would still predict their existence.

And that’s because we have a truly excellent model for sex development 😉