Extinction of a species is often thought to be something negative and should be prevented at all costs, but what if we’re talking about the extinction of a “bad” species such as the malaria-carrying mosquitoes, Anopheles gambiae?Malaria is a disease caused by a parasite which affects the healthy development of your red blood cells by infecting it. And how does a parasite get to your red blood cell? Well, A. gambiae has been known to be the primary and one of the most efficient vectors (organisms that carries and spread the diseases from one host to another) that transmits malaria amongst humans. Basically, what the mosquito does is that while it bites you to get its lunch, it also releases the parasite into your bloodstream to infect you.
Now, did you know only female mosquitoes feed on blood? Normally, mosquitoes only feed on things like nectar of plants and water to get the necessary nourishment they need to survive. But because these female mosquitoes need protein to produce their eggs, they must seek alternative food sources which in this case, is our blood.
Since female mosquitoes are the problematic ones that feed on blood and causes transmission of malaria, preventing the reproduction of female mosquitoes would greatly help in reducing the spread of malaria. At the same time, the lack of female mosquitoes would mean there will be less mosquito eggs being laid, reducing the population as a whole. This is where the research study conducted by the team from Imperial College London comes in.
In the study, the scientists used a genetic engineering tool known as the gene drive. These gene drives work by using the CRISPR-Cas9 technology more commonly known as the “molecular scissors” to cut off a region and disrupt the doublesex gene in charge of the determination of sex in the mosquitoes. Although the results showed that male and female mosquitoes which inherited only one copy of the disrupted gene are unaffected and managed to develop normally, females which inherited two copy of the disrupted gene developed some male-specific features and abnormal proboscis (which they use to feed on blood). These abnormal features caused the affected females to be unable bite and feed on blood, which resulted in the inability to lay eggs.
So you may be thinking, a gene can only have 50% chance of getting inherited as only one of the two chromosomes from each parent will be passed on to their offspring, so how does this disrupted gene get inherited so much that it totally prevented even a single mosquito from laying eggs and causing an “extinction”? And this is what’s special about the mechanism of the gene drive. Gene drives consists of the Cas9 gene that produces a protein which are able cut up a region in the gene. So even when the mosquito only inherited one copy of the disrupted gene consisting of the gene drive, proteins will still be produced to cut off the specified region on the other “healthy” chromosome. This causes more mosquitoes having two copies of the disrupted gene which will eventually lead to almost 100% of mosquitoes inheriting the disrupted gene. This means no mosquito will be able to lay eggs and produce a new generation of mosquitoes, causing extinction in the population.
This study was the first to observe this extinction caused by 100% of the mosquitoes in two different cages eventually inheriting the disrupted genes and stopped producing eggs at the 8th and 12th generation respectively. According to World Health Organisation, almost half of the world’s population is at risk of malaria and there were approximately 212 million malaria cases with around 429 000 malaria deaths in 2015. Given that malaria is capable of causing such high death rate in the human population, this new research finding may potentially be the hope for many lives.
While this may possibly be the end to the malaria-carrying mosquitoes, it is still important to note that the findings were observed in a well-controlled lab environment. When applied to the natural world, there will be many factors which will affect the inheritance of the gene drive.Even so, I would say this is still a big step towards living in a world free of these harmful malaria-carrying mosquitoes.