Somewhere along this somewhat Quixotic attempt to earn a PhD, I took it upon myself to make transheterozygotes in the fruit fly. This isn't all that difficult a task, in retrospect, but never having worked with fruit flies (aside from a brief and disastrous stint as a senior in high school), this is a bit more challenging than I'd initially thought.

But really, the challenge is in the learning, and after learning the details, it's much easier. Fruit fly females need only mate once their entire lifetime, during which they are able to store enough semen for fertilizing the entirety of their unfertilized zygotes. So my job, really, is to pick out virgin females of one genetic background (which is a bit more difficult than it seems in some instances and genetic backgrounds) after which point it's just a matter of getting the male and the female alone for an appropriate amount of time.

And, to be brutally honest, preventing fellow members of the Animalia kingdom from having sex has never really been an issue.

But this is not what this post is about--really, it's about the word transheterozygotes. For those wondering, they're a lot like heterozygotes, only different.

To be sure: heterozygotes refer to the state of one allele in an organism. Suppose there are two alleles of a single gene, designated A and a. A diploid organism (an organism, much like humans, with two copies of the genome) with two copies of the A allele (AA) or two copies of the a allele (aa) are called a homozygote. A diploid organism with one copy of the A allele and one copy of the a allele (Aa) is called a heterozygote.

So where does this transheterozygote business come in? Suppose I were to have two different mutations in the A allele, designate them A* and A^. So we can now have different types of heterozygotes: AA*, AA^, both of which we call heterozygotes, and A*A^, which we call a transheterozygote.

Why call this latter combination a transheterozygote (as opposed to a heterozygote)? The reason (at least to me) isn't exactly clear:

That is to say, of course, that the reason is clear: we call A*A^ a transheterozygote (as opposed to a heterozygote) because it's a combination of two mutant alleles. But implicit in this designation is a supposition that one of the alleles is naturally occuring, while the other allele is somehow man-made.

But what's moreover interesting in this assumption is that we've implicitly defined normalcy and "naturality" by mutations that were present the progenitor of the model organism--that was ground zero, and any changes we make to it's genome we'll call "mutations." Combinations of these mutations we'll designate specially (as transheterozygotes¹).

And note the beauty of this with respect to other atrocities: "all natural" foods and shampoos, people who claim not to like "chemicals" in their food, "organic" produce. It's really quite dizzying the extent to which those paltry words seem to make things so much better--odd they should play a role in genetics too.

¹Interestingly, there is no such thing as a cisheterozygote. By extrapolation, I suppose, a cisheterzygote would be the same as a wild type (or normal) organism. Or perhaps a homozygote? I don't know. My head hurts.