Something I Learned Today: Gene Drive

Genetics is something I only have a passing acquaintance with. When it comes to stuff like this, I have to start researching just to get a handle on the words used by people that actually work in the field.

But I ran across something very interesting today: The idea of gene drive. My initial confusion came because I didn’t understand how the word “drive” was being used. My first mental picture was of something like a hard drive for genes. But it’s not used as a noun. It’s a verb, as in a force. So gene drive is an action not a thing.

It also turns out this action is related to the hereditary transfer of a trait. This matters to the scientists because if they’re studying a particular trait, there’s only about a 25% chance the trait will pass to offspring. This idea is taught in grade school using Mendel’s pea plants, and the resulting Mendelian inheritance.

So the idea of gene drive came about because researchers wanted to speed up the process. If the goal is to study a gene in fruit flies, first the parent’s genome is hacked. Then the offspring are studied. The 75% or so that don’t inherit the gene are not needed. I’m not going to shed a tear about having to dispose of fruit flies, but in mammals it’s literally a bigger problem.

When I was little, our family knew a couple that raised rabbits. Show rabbits of all things. They had a certain fur pattern registered with whatever rabbit breeding association they belonged to. Some of the rabbits won awards. Those lucky ones lived out their lives breeding, well, like rabbits.

The wife was in charge of the breeding, her husband dealt with the rejects. Mendel’s laws hit home pretty fast. Around two-thirds of the offspring didn’t inherit the pattern. The rabbits also had to grow up some before she could make a decision about their pattern. The end result was a lot of unwanted rabbits.

Sadly, an individual rabbit has no commercial value. As for adoption, that’s only for baby bunnies. No one really wants a almost-grown rabbit. So the ones that weren’t breeding stock became meat. At first the husband took them to the butcher. Soon the cost started to add up, and he learned how to do the job himself. I learned all this once the rabbit started showing up on our dinner table. My father did some work on the husband’s car and got paid in rabbits. That car needed a lot of work. We ended up eating rabbit for most of that summer.

While researcher studying fruit flies might not need to hire a butcher, the problem remains. They still have to breed many more offspring than needed. If they’re studying multiple traits, the number of offspring needed is much larger. All of this takes time, money, and lab space.

The goal then is to “drive” the genes into the next generation at a higher rate than Mendelian inheritance. With more of the offspring having the desired trait, the research can progress faster.

I found out about this today because some biologists brought it up on Twitter.

Gene drive experiments started out on mosquitos with the goal of making them unable to carry the malaria virus. Mosquitos also die off every season. To have an effect on the disease carrying population, a higher-than-normal rate of inheritance was needed.

The original method used endonuclease genes that spread rapidly, but only within a genetically modified population. The traits are inherited at a higher rate. But still required multiple generations to see a high number of offspring have the trait.1

Then CRISPR came along.

Editing DNA using this method essentially became cut and paste.2 This week a paper was published that shows how using a CRISPR method called Mutagenic Chain Reaction3 (MCR) can get close to 100% trait inheritance in the next generation.

This is also quite controversial. The traits edited into a genome using MCR can be passed on to populations in the wild. The fear is that a runaway mutation could spread uncontrollably. Like the plot of a bio-disaster movie.

All of this, both CRISPR and MCR are very new. Cross and selective breeding has been with humanity since we stopped hunting and gathering and started farming. Actual gene-splicing in the laboratory has been with us for all of this century. But having grown up with this in the world, I have never given much thought to the “next.”

By next, I mean the thing that happens after the gene-splice/edit/deletion is done. In the scare-narrative the thing that’s modified then flips out and kills everyone. In reality the thing that modified doesn’t do much at all. Its job is to pass the new trait on to the next generation.

That’s the part I never had any reason to consider. The news about genetics never really mentions this aspect. I don’t think I’ve ever seen a popular news article mention how many generations it takes to get the results that are reported. Now I have at least a limited understanding about what happens after the genetic modification happens. Sometimes Twitter really is worth a damn.

I started out wondering what gene drive was. Now I know someone just discovered what I thought was already being done. Go figure.

  1. In this study, after 10-12 generations about 60-80% of the offspring carried the trait.
  2. A gross oversimplification, but accurate enough for non-biologists.
  3. Researchers need to realize that people would be less scared of science if the names weren’t so scary.