Peter Attia, M.D.

Yeah, the testosterone at this point is the determining factor.

Determining what?

Muscle mass, body hair, things like that.

Although that's also an easy experiment to do.

You could imagine giving a male a 5-alpha reductase inhibitor from birth.

Like as a thought experiment.

Yeah.

If you took a normal, chromosomally, phenotypically normal male, and from the time they were, call it five years old, you just gave them 5-alpha reductase inhibitor.

All you're doing is turning their DHT down to zero and doing nothing else.

You're basically asking the question, will they develop normal musculature?

How did they get an IRB for that?

Yeah.

Interesting.

Okay.

So you and I are probably the only ones at this point, this excited about this discussion because we're now so far down the weeds of embryology, but bringing it back to the surface, the takeaway here is that XXXY start out for about five weeks, indistinguishable at about that five week mark.

a gene on the Y chromosome specifically begins to trigger the differentiation pattern.

That differentiation pattern triggers the transcription of genes that turn on hormones that are going to further activate and drive sex differentiation.

But if that were true, it must be more complicated or else you wouldn't have Turner syndrome.

Which we can define for folks as single X chromosome, which presumably they got from mom and then they didn't get a chromosome from dad.

Or do we know that?