Andrew Huberman· PhD
Now, the goal of fertilization is to bring that egg cell into close enough proximity that it can be fertilized by a single sperm cell. And that sperm cell will bring 23 chromosomes, as well, that include-- just as in the female egg, it'll have 22 autosomes and one sex chromosome. And in the male, that sex chromosome can either be an X chromosome, which then would give rise to female offspring, or a Y chromosome, which would give rise to male offspring. But just to give you a sense of how X chromosomes and Y chromosomes can actually accomplish that sexual differentiation, both of body and brain. I'll just mention in two sentences that, for instance, if there's a Y chromosome as opposed to an X chromosome, that Y chromosome contains genes that suppress, for instance, the development of female genitalia and thereby give rise to male genitalia. So rather than the formation of a clitoris, it's the formation of a penis. And rather than the formation of ovaries, the formation of a testes. So that's more directed towards sexual differentiation. We're not going to get into that right now. We'll get into that in a future episode. But even if you're only tracking about 10% of what I'm saying right now, I promise you're doing great. If you're tracking more than 10%, well, then you're doing terrifically well, because the essence of fertility and fertilization is to bring together that haploid cell that is the sperm that only has 23 chromosomes-- but not pairs of chromosomes because that's the DNA from dad-- together with the egg, which, as I told you already, has 23 pairs of chromosomes. So part of the fertilization process has to be to get rid of one half of those 23 pairs in the female. You got to get rid of it, and you have to get the egg