Scientists on Monday revealed that they could hoodwink the laws of evolution: They have come up with a way to force a gene that kills malaria parasites to spread through an entire population of mosquitoes that usually carry the parasite – at least in a lab. Hypothetically, no malaria in mosquitoes means no malaria in people either. This is all possible thanks to a disputed new technology known as a gene drive. Or Crispr. Or both.
Let’s take a minute to explain which is which, as well as their differences.
Let’s begin with gene drives. Scientists have been playing with this idea, theoretically at least, for decades. A “gene drive” is a general term for anything that makes a gene spread quickly through a population. A typical gene has a 50/50 chance of being passed on from parent to offspring. A female mosquito has two copies of the eye colour gene – for example, red and not red – one of each on a pair of chromosomes. The female mosquito passes one copy of each chromosome to each of her offspring, hence 50/50.
Therefore, if you are an overachieving and clever gene, you will want to copy yourself onto the other chromosome as well. You want mother mosquito to be either red/red or not-red/not-red. In certain circumstances, when chromosomes get injured, the cell’s natural DNA-repair system uses the uninjured chromosome as a template for repair. Then the gene drive duplicates it into the right place on the other chromosome.
Inspired by natural gene drives, Austin Burt – the geneticist – suggested in 2003 making a synthetic one to use a gene that kills the malaria (present in mice) and spread it into mosquitoes. However, the suggestion remained theoretical due to the fact that scientists were ensure of how to get a self-duplicating gene to cut a chromosome and reliably duplicate itself as well as a long malaria parasite-killing gene beside it.
A much hyped genome-editing tool called Crispr/Cas9 came along in 2012. Crispr/Cas9 is basically a pair of highly targetable DNA scissors. Scientists published a method to make gene drives that uses Crispr/Cas9 cutting enzyme in fruit flies, earlier this year. Yesterday, scientists reported that they could utilize a similar gene drive in the mosquito that carries the malaria parasite – the Anopheles stephensi mosquito.
The gene drive part is vital. It permits the anti-malaria gene to continue spreading through procreation and from generation to generation, even if its results contain no reproductive benefit for the mosquito. (Generally, that is the rule used by evolution to decide which genes get passed down.) Another gene drive idea is to alter the balance of sexes for mosquitoes – more of one than the other. This carries disadvantages for the mosquito but plenty of potential positives for humans.
However, we haven’t beat malaria yet. Creators of the gene drive are proceeding cautiously, and have no strategies to release the gene drive systems into the wild. As you can guess, messing with the genomes of an entire population and evolution leads scientists to worry about unpredictable consequences. Actually, a different research team announced recently that they had created gene drives that eliminate edits from another gene drive as a safety precaution. However, they have not released their anti-gene-drive gene drives either.