In a breakthrough for malaria control, researchers at Imperial College, London, have created a strain of the Anopheles gambiae mosquito that produces 95% male offspring—bear in mind, only female mosquitoes bite and the female Anopheles is a carrier for the malaria pathogen, Plasmodium. The researchers, according to a report in Nature, found that flooding cages of normal mosquitoes with the new strain caused a shortage of females leading to a population crash. The researchers transferred a “sex-distorting” gene from a slime mould to the A. gambiae specimen. This gene is responsible for the formation of a restriction endonuclease—an enzyme that cleaves DNA when it recognises specific nucleotide sequences—for the X-chromosome. Thus, the genetically modified (GM) males could almost pass on only Y-chromosome containing sperms as the X-chromosomes got shredded during sperm production. Note, in the natural process, the distribution of X- and Y-sperms is 50-50. Since eggs have just X-chromosomes—and XY pairing results in males while XX pairing results in females—introduction of 150 GM males in five cages with 50 normal males and 50 normal females caused the number of females to plummet drastically in four generations.
What is very promising is that the genetic modification is inheritable, making it a self-sustaining effect. A genetic intervention in the wild scores over the traditional mosquito-control methods, chief of which is pesticide use, because this method will selectively eliminate just one vector species. However, given how a genetic intervention of this kind would need multiple top-ups to eliminate the vector, tackling malaria in the interim would require developing a vaccine. So, the new GM technology should add to the cheer from the recent discovery a vaccine candidate by researchers at the Indian Institute of Science, Bangalore.