Nick Lane: evaluation

Transcript context

…You have this really interesting discussion about how this not only explains why there’s two sexes, but the particular differences in why eggs and sperm developed the way they do, why there’s different amounts of replications before they are mature, et cetera. I wonder if we can recapitulate that. So as soon as you’ve got this fundamental difference, even in single-celled critters, that one of the sexes passes on the mitochondria and the other one doesn’t… Males do not pass on their mitochondria. This is beginning to explain differences in multicellular organisms between the sexes, between the nature of the germline. In some sense, men do not really have a germline in the sense that women have a germline. In the female germline, you make these oocytes and you put them on ice effectively. You look after them, you switch them off as much as you can, you try and protect them from mutations, you mollycoddle them effectively. Whereas men just mass-produce sperm full of mutations. There’s a lovely phrase from James Crow, who’s a geneticist: “there’s no greater genetic health hazard in the population than fertile old men.” So why would you go on mass-producing sperm all the time? Part of it is you don’t have to pass on the mitochondria, so you’re freeing yourself up to mass-produce sperm. Some of them are full of mutations, but a lot of them aren’t. You mass-produce them and the chances are it’s going to work out okay because the ones that can swim best, for example, are the ones that are more likely to… That’s not strictly true, but you can imagine it along those lines. But in the case of the oocytes, in the case of the egg cells, you’re passing on those mitochondria. You don’t want to be accumulating mutations in that mitochondrial DNA. You want to switch them off as much as possible, keep them on ice as much as possible. Very much the differences between how the sexes end up becoming different to each other, boils down to what are the constraints on your reproductive system. Let’s talk about the Y chromosome, which is also not recombined. Just the same way that female egg cells try to minimize the amount of duplications in order to preserve the quality of the mitochondrial DNA and prevent errors, why isn’t the same thing happening with the Y chromosome? Shouldn’t all this sperm duplication be resulting in all kinds of errors in the Y chromosome?…

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