A quick introduction to gene drives
The future is exciting. With current advances in biotechnology and genetic research, it is becoming possible for humans to intentionally change entire ecosystems, wipe out invasive species, and edit organisms to prevent disease — all with the power of gene drives.
What are gene drives?
A gene drive is a type of genetic element which biases itself into future offspring in a manner inconsistent with Mendelian genetics. Therefore, a gene drive can improve its chances of being present in future offspring with each generation, beyond what would be considered normal. This has enormous implications. Even though gene drives occur naturally, artificial gene drives can genetically edit species for population control or to force the species to express some desired trait.
It’s also important to note that the term “gene drive” doesn’t refer to one specific technology. There are plenty of different gene drives created via widely different mechanisms. All gene drives have one thing in common — they give a selected gene a much higher chance of being inherited than would be typically expected.
How can we use gene drives?
Gene drives propagate any gene we want across a given species. Target Malaria is a project in sub-Saharan Africa currently investigating wiping out malaria via gene-driven mosquitos. Gene driven mosquitos are unable to carry malaria. At the time of this writing, malaria places a massive burden on many African countries and is responsible for millions of deaths yearly. Gene drives could further edit organisms that carry diseases such as dengue and yellow fever. We could even make gene drives in an invasive species to force them to give birth solely to male offspring — wiping the species out after enough generations.
So, what are the risks?
Gene drives give us the ability to make sweeping changes to an entire species — so there are tons of risks. Gene drives can potentially spread among species via interspecies breeding — leading to unintended consequences like the collapse of a wanted species. Additionally, once released into the wild, it is hard to undo a gene drive unless acted upon immediately. Suppose we use a gene drive to wipe out an invasive species of fish in one of our lakes. We could create a gene drive which makes the mutant only give birth to males, or only lay infertile eggs. As the gene moves through the species, fewer and fewer females or offspring will exist until the gene drive exterminates the population. If one of those fish were to escape and get to a location where that fish is a wanted, native species, we could unintentionally devastate that species in a place where it should exist.
So why don’t we use one?
Well, it’s not so simple. Since most species are parts of ecosystems that are international, any release of a gene drive should first be agreed upon by all nations that might be affected by it. There are hundreds of mosquito species, and only a handful of those species are capable of transmitting malaria to humans. It’s tempting to release a gene drive into those species to wipe them out completely. But what happens to all the other organisms in our complex ecosystems which rely on those mosquitos for food? What started as a noble undertaking might lead to a cascading effect with unintended consequences.
Gene driven organisms (GDOs) classify as GMOs. As such, they must pass all legislation for GMOs in order to be released legally. It’s also essential that all nations have a say in releasing a GDO that might affect them — taking careful negotiation and time.
Are gene drives 100% effective?
Well, probably not. Gene drives most likely incur a fitness cost on the organism. That means that the presence of the gene(s) driven into that organism reduces its ability to survive and have offspring. The same natural selection laws occur, even if the gene drive can propagate through a population regardless of whether or not it harms the host. Natural selection might produce some mutants in the population resistant to the gene drive — rendering the gene drive useless.
Can we undo a gene drive?
The quick answer is maybe. We could make a gene drive that undoes another gene drive. Many organizations believe that no gene drive should be released if it doesn’t also have a counterpart gene drive that counters it. The problem is that gene drives don’t typically get to every organism in a species. Therefore the counter gene drive wouldn’t reach every organism either. As such, the counter gene drive to undo the original one won’t get to every organism with the original drive. There are also the risks associated with the counter gene drive. The counter gene drive carries the same potential for unintended consequences in the target species as the original gene drive did.
How many different types of gene drives are there?
A lot. The most common type of gene drive scientists are talking about is the “homing drive,” but there are also tons of others, such as toxin-antitoxin, under dominance, split drives, and sex-biasing systems. This article is just a quick little introduction, and as such, I won’t get into the details of all of these drives here. However, I highly encourage you to look into gene drives and the various types there are to give yourself a better picture.
If this article has sparked your curiosity, I highly recommend the TED talk below. It’s only 12 minutes and is very informative.
And as always -
