Carole Hooven, Ph.D.

So what's really cool and interesting is that before that time, we all have a gonad that can become either one.

It can become testes or it can become ovaries.

And that's sort of an amazing design.

That's evolution's way of not wasting energy, not having to have two different systems that one develops and the other gets discarded, at least in terms of the gonads.

So they come first.

So in terms of sexual differentiation, that means that for XY individuals, the gonads are going to develop along the testicle route.

And without the SRY gene, they will, by default, when I say by default, that doesn't mean that nothing else has to happen.

Other genes have to be expressed.

And that's an active process.

It's not a passive process.

But without the SRY gene, those undifferentiated gonads will differentiate in the female direction to form ovaries.

Yes, in some ways that is true.

I would not put it that way, but it's by default.

The individual will develop, say, female.

You will be chromosomally male, sure, but you won't develop functional ovaries because you need two Xs to do that.

Yes, yes.

So your external genitalia would appear to be female.

we'll get into those cases.

But yeah, if you think about what the genitalia look like in an early developing fetus, it looks female.

It doesn't have to change that much.