Nick Lane: prediction

Transcript context

…It might be worth explaining why it is the case that sex is preferable to lateral gene transfer in the sense of systematic pooling and parallel search across gene space. If there is this advantage of sex and bacteria have some antecedent to it, why didn’t they just get the whole thing? Is it just that it’s not compatible with their size? I think they had no need for it. What they do is lateral gene transfer. Basically you pick up random bits of DNA from the environment. It can be a bit more sinister than that. You can kill the cell next to you and take its DNA and load that in. That does happen, but for the most part, you pick up bits of DNA from the environment. It’s usually small pieces, usually one gene’s worth or something. You’d only do that if you’re a bit stressed. If things aren’t going well for you, you will then pick up bits of DNA, bind it into your genome and hope for the best. For most critters, most of the time it’s not going to work, but for one of them it does, and they will take over. It speeds up adaptation to a changing environment. Why are they only using one gene? There’s two ways of seeing this. You’ve got a bacterial-sized genome, it’s pretty small. You’re going to replicate faster if you keep that genome small. It’s kind of a disadvantage to have a big, unwieldy genome. Eukaryotes have that. It’s an interesting question. Why would you have such a big, unwieldy genome that takes longer to copy? Bacteria are really streamlined. They get rid of genes they don’t need and then they can grow faster. But now the conditions change and now you need this gene. So what do you do? You pick it up. You just pick up random genes and hope for the best, pick up the right one and off you go again. Bacterial genome sizes are small. They’ve got what you’d say is a small genome, but then a large pan-genome, which is all of the genes they have access to. So an E. coli cell might have 3,000 to 4,000 genes in a single cell, but access to 30,000 to 40,000 genes. What is keeping the metagenome around? Why doesn’t everybody just converge to this streamlined thing that is needed for the current context?…

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