Balance of nature: gene drives are a worry (Introduction)

by David Turell , Friday, June 17, 2016, 20:46 (3080 days ago) @ David Turell

A solution to everlasting gene drives is to use ones that last for only a few generations:-https://en.wikipedia.org/wiki/Carina%E2%80%93Sagittarius_Arm-"It's a Catch-22. We have to field-test gene drives to determine if they are safe to use to stop the spread of malaria, for example. But these bits of self-copying DNA could spread to every member of a species, making field tests risky. “A release anywhere is likely a release everywhere,” says Kevin Esvelt at the Massachusetts Institute of Technology.-"But his team may have the answer. It has come up with a way to make gene drives self-limiting, so they spread rapidly through a population at first but gradually vanish after, say, 50 or a hundred generations.-"Not only could this make it possible to safely test gene drives in the wild, it could also allow cities and countries to use them locally without have to worry about the risk of worldwide spread.-"Most plants and animals have matching pairs of chromosomes, but pass down only one of each pair to each of their offspring - the other comes from the other parent.-"This means that if you add a piece of DNA to one chromosome, normally only half the offspring will inherit it. Gene drives cheat by “copying and pasting” themselves to the other chromosome, meaning all offspring inherit them and they can spread rapidly throughout a population.-"Natural gene drives have been around for hundreds of millions of years. In the past two years, biologists have created artificial versions based on the CRISPR gene editing system.-***-"To create gene drives that don't spread indefinitely, the team split them up into three or more parts - which Esvelt calls elements - to create a “daisy chain”.-"Each element contains one or more genes that contribute towards the whole gene drive. In Esvelt's design, element A can only copy and paste itself if element B is present. Element B can only copy and paste itself if element C is present. And element C, crucially, cannot copy and paste itself at all - it can only spread by normal breeding, to half of offspring.-"The idea is to release thousands of mosquitoes, say, carrying all three elements. When they mate with wild mosquitoes, all the offspring will inherit element A and B, but only half will inherit element C. In the following generations, element B will spread rapidly and A will spread even more rapidly, but C will gradually die out. Once it does, B will start to disappear, and finally A will too.-***-:The team's modelling suggests that if only a few animals are released, the drive's spread would be limited and it would soon die out. If enough animals are released, though, element A could spread to 100 per cent of a local population. And by adding more elements to the daisy chain, the gene drive could be made to persist longer in the wild.-"This could allow local use of gene drives. Suppose the US wanted to release a gene drive that would halt the spread of Lyme disease by making the white-footed mice that carry the disease-causing bacterium immune to it. A conventional gene drive would spread to mice in Canada and Mexico, so approval from their governments would be needed too. With a daisy-chain drive, the spread could be limited. Esvelt is exploring the possibility of combating Lyme disease this way but stresses that it is a long way off.-"Another possibility, he says, would be to use a daisy-chain gene drive to help save Hawaii's native birds, which are being wiped out by avian malaria. The gene drive could be used to eliminate the mosquito species that carries the disease.-"With a conventional gene drive, a single mosquito stowing away in someone's luggage could spread the drive around the tropics. If the daisy-chain drives work as planned, a single mosquito couldn't spread the drive very far at all."-Comment: Interesting research, but it doesn't solve the problem of how speciation works, not that it was meant to. But it is possible that natural gene drives exist and drive speciation.