Transcript:

Viruses Mistakes R Us Viruses reproduce by invading a cell and making copies of themselves lots of copies. But in the process of copying their genome, their genetic blueprint, they often make bad copies, which turns out to be a good thing for the virus. I'm Jim Metzner and this is the Pulse of the Planet.McDonald: One of the ways the virus changes is during this genome replication process.Sarah McDonald is an assistant professor at the Virginia-Maryland College of Veterinary Medicine and the Virginia Tech Carilion Research Institute. McDonald: The virus's enzymes, the molecules that actually are the ones that copy the genome, make lots of mistakes. This is in contrast to our own host cell enzymes that copy our genome. Every time our cells divide, we need our DNA in one cell to be fully copied and separated into the other cell. And you want that process to happen with really high fidelity, because when it doesn't happen with high fidelity, you get cancer.Viruses don't necessarily care if they have a lot of mistakes in their genomes. If the virus makes 3 mistakes out of every 1,000 positions that it copies, we now have a whole swarm of viruses, each of which consists of different variantsc that have different levels of mutations in them.Now, what happens then is some of these variants in the population have an advantage. Say there's a million viruses in this swarm of mutants, essentially, and one of them has a change that now allows it to be transmitted, say, from a pig to a human. It's a pig virus, and now, all of a sudden, that one variant can infect a human cell. Well, it opens up a whole new host species, and that virus is then going to have an advantage within the human. I'm Jim Metzner and this is the Pulse of the Planet.