The controversy primarily comes from the applications of CRISPR-Cas.
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.
Actually, none of the controversy comes from applying CRISPR-Cas, since that's just a boring technology part that simplifies something which could have been done using more tedious mechanisms.
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.
"even though the trait isn't necessarily evolutionary beneficial for the organism."
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.
If the trait is completely neutral it will double every generation (until saturation is setting in). If the trait is like 10% negative then it will instead increase by a factor of 0.9*2 = 1.8, which is still pretty quick.
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.
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.
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."
I'm not sure but I think the 99.5% figure here is for breeding modified mosquitoes with ordinary mosquitoes. That's the idea of the gene drive method. The spread of the gene has to be better than normal mendelian inheritance, otherwise it would never spread throughout the population in the first place...
Exactly. So suppose at some generation, the fraction of mosquitoes with the modified trait is p (and the unmodified fraction is 1 - p), and suppose that all mosquitoes are equally fit.
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).
That's one way to do a blood transfusion. Imagine a cloud of tiny insects surrounding 2 people, transferring blood from one to the other a drop at a time.
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.
Not exclusively, but indeed the two main vectors for both dengue and chikungunya are Aedes aegypti and aedes albopictus. Several other species are at least somewhat capable of transmitting these viruses.
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.