Carole Hooven, Ph.D.

So there's temperature-dependent sex determination.

So people should not confuse the sex hormones themselves with the definition of sex.

Sorry, chromosomes.

Thank you.

In mammals, the chromosomes determine sex, but do not define sex.

Again, across almost all sexually reproducing organisms, it's the gamete type that the organism is basically designed around, that the reproductive system is designed around, that defines sex.

Other organisms can be hermaphroditic, produce both gamete types at the same time, or they can be sequential hermaphrodites.

So I just want to get that out first.

So in humans, the mother's egg, the sex chromosome is always going to be an X that it donates in its egg, and it's going to combine with a sperm.

50% of the sperm are going to have a Y sex chromosome, and 50% of the sperm are going to have an X.

in general.

Those two combine and the developing embryo is going to be either XX and XY.

So let's just start with the XY.

So you were an XY.

I had a son who was an XY, which is weird for women because they will have something inside of them that has testicles that produce testosterone, which I think is interesting.

So an XY fetus around five or six weeks.

I should just say that XX and XY are both, they're almost identical until that time.

And the Y chromosome has a gene on it called the sex determining region of the Y chromosome that produces a protein called the SRY protein.

And this is a very important gene.

Protein because it triggers the differentiation of the undifferentiated gonad.