'Anti-malarial mosquitoes' created using controversial genetic technology
theguardian.com
theguardian.com
In a sense the technology is like nuclear material: it can be used for ill; it can be used for good; and it can cause harm even if trying to do good. But this is also true of our more modest applications of human ingenuity and power, such as civil engineering. I am choosing the nuclear parallel because of the wide-ranging impact that facile genome editing will have - both positive and, inevitably, with some negatives.
It's the gene drive part that's controversial.
It refers to making sure all children (and grandchildren etc) inherit a trait, even though the trait isn't necessarily evolutionary beneficial for the organism. The way this is implemented in this case by having a gene that codes for proteins that insert the gene in chromosomes that do not already have it.
This means that by just releasing a few specimen with the gene drive, the entire population can be gene modified in not-that-many generations. A year may be sufficient for insects, since their generations are so short.
If the trait is negative, it will be selected out of the population. It's only if it's beneficial, or neutral, that that it will spread. What's particularly special about gene drive, is that it drives itself onto 100% of progeny, rather than the 50% expected by traditional mendellian genetics.
Only if it is extremely negative, by more than halving amount of offspring, will it be selected out.
That's in the short term. Presumably, some sort of resistance would evolve in the long term.
At the very least, this experimentation is likely to show some interesting real-world population genetics that we can measure.
Anopheles females in tropical conditions take around 12 days to go from egg to adult.
So if that's true, even if you could wave a magic wand and replace the entire mosquito population with these at one time, less than half of the population will still have the trait at the five year mark.[0]
Compounding is a bastard.
Though sure, the one-time magic wand doesn't resemble how this would be rolled out, but the general point is that the more frequently some species breeds, the harder it is to mess with.
[0] 0.995^x = 0.5 -> x = 138.2 generations. 138.2 * 12 days / 365 = ~4.5 yrs.
A random child in the next generation will have the modified trait if: (a) both its parents are modified. This happens with probability p^2 (b) with probability .995 if one of its parents are modified. This happens with probability 2p(1-p), for a total probability of 1.99p(1-p).
Overall, the fraction of modified mosquitoes in the next generation will have p^2 + 1.99p(1-p).
Plotting this versus the identity function (http://www.wolframalpha.com/input/?i=%7Bp%2C+p%5E2+%2B+0.995...), we see that this will increase monotonically to p = 1 (all mosquitoes have the modified trait).
Because almost all the progeny carry the new genes, instead of just 50 percent as would be expected by Mendel’s laws of genetics, the inserted genes are expected to spread rapidly and take over a wild population in as few as 10 generations, or a single season. A large region, at least in principle, could be freed from malaria, which kills almost 600,000 people a year."
Actually, I'm not sure about chikungunya, but Malaria and Dengue is carried by different species of mosquitoes. I think chikungunya is carried by the same species as Dengue, but I'm not sure if that is exclusive to that species.