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Of course, James and his colleagues are far from the first to try using genetically engineered mosquitoes to defeat malaria—and other mosquito-spread diseases, such as dengue. But the infectious genetic trick sets these mosquitoes apart. Whereas other modified mosquito strategies would require periodically releasing large numbers of engineered insects to make sure the genetics take hold in a wild population, these new mosquitoes can theoretically take over a wild population completely, forever—which is good, but also worrying to some.
That controversial infectious DNA construct is a type of CRISPR/Cas9 gene drive system, which contains several genes that allow it to insert itself into a chromosome and make mosquitoes resistant to malaria parasites.
The CRISPR/Cas9 system, winner of the 2015 Breakthrough Prize, directs the cutting and pasting of the construct into a chromosome. Basically, the system works by having an RNA molecule that’s engineered to recognize a specific spot in the mosquito genome. Then, the Cas9 enzyme snips that spot. Natural DNA-repair mechanisms will try to patch up the broken DNA using a template that contains a similar DNA sequence. Because the rest of the mosquito gene drive system is engineered to contain similar sequences to those naturally found near the snip-spot, the mosquito’s repair system is tricked into using the construct as the patch. Thus, the whole gene drive system gets copied and inserted into the chromosome.
In addition to the CRISPR/Cas9 system, the construct also carries two genes that make the mosquitoes resistant to P. falciparum, one of the parasite species that causes malaria in humans.
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