Natural selection only makes features more common if they help organisms survive or reproduce. But we could get around that restriction by accelerating evolution using something called a ‘gene drive’.
Gene drives are bits of DNA that work by breaking the laws of inheritance. Many organisms inherit genes on pairs of chromosomes, one from each parent, so their offspring have a 50/50 chance of inheriting either the maternal or paternal copy of any given gene. But a gene drive can copy-and-paste its DNA sequence from the chromosome carrying it to the other chromosome, ensuring the drive is passed on to 100 per cent of an organism’s offspring. Over multiple generations, the drive rapidly spreads through a population’s gene pool.
The prospect of modifying an entire population was once limited by naturally occurring drives, which can only copy-and-paste themselves to certain locations. But by using a gene-editing system called CRISPR, scientists can design artificial drives to target a specific DNA sequence. Such an achievement was unthinkable a decade ago. “No one even imagined that we might be able to readily edit entire species,” says evolutionary engineer Dr Kevin Esvelt of MIT. Esvelt built the first CRISPR gene drive in yeast and showed you can target and overwrite a previous modification, meaning the effect of a gene drive is reversible.
Gene drives could eradicate diseases like malaria, which killed 445,000 people in 2016. Malaria is caused by blood parasites transmitted to humans via bites from infected female mosquitoes. One approach is to suppress insects by blocking reproduction. This is being tested in the lab by the Target Malaria project led by geneticist Prof Austin Burt and immunologist Prof Andrea Crisanti of Imperial College London. In 2018, the researchers used gene drives so that female mosquitoes became infertile and, after eight generations, the captive population crashed. In the wild, this ‘suppression drive’ could collapse mosquito numbers below the level that’s necessary to sustain malarial parasites.
Drives could also protect organisms. In farming, an ‘alteration drive’ could genetically alter pests so they dislike the taste of crops. This would eliminate the need to spray fields with toxic pesticides. In wildlife conservation, gene drives could attack invasive species – like rats, a major cause of extinction on islands – that threaten endangered organisms.
But gene drives could cause harm. A mathematical model built by Esvelt’s team predicted that a drive that spreads indefinitely will escape beyond its target population (due to animal migration, accidental or deliberate release) to other areas. Unless you’re aiming to drive species extinct, it’s better to deploy a self-limiting drive with temporary – and likely local – effects.
Despite potential risks, Esvelt says we should be excited about gene-drive technology. “It’s a way of using nature’s tools to solve ecological problems.”
This is an extract from issue 330 of BBC Focus magazine.
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