Eli5: Is there a scientific optimal sweet spot for most genetically robust offspring?

Question

We see in wildlife mules, ligers and tigons as example of genetic dead end offspring as their parents were genetically too distinct

At the same time offspring from genetically too similar parents : siblings cousins etc produces an offspring with bad genes

What is the goldilocks zone genetically that is considered just right? Is it the same or different among species?

In: 3

Answer 1

Probably, but nobody at this point would ever predict what it is, for any particular species.

In plants, [heterosis](https://en.wikipedia.org/wiki/Heterosis) or hybrid vigor is an extremely, extremely common phenomenon. It would be surprising if there weren’t some kind of equivalent that affected most species to some degree. Breeding programs essentially work by making a prediction “this is the sweet spot for the most genetically-robust offspring”, and then you breed plants to try and make that happen. And then you see how well it worked, and you keep on going from there in an iterative process that generates improvement.

And breeding programs work very well, but the problem is that there’s actually no way to just outright perfectly calculate an organism’s phenotype (observable traits) on the basis of its genotype (genetic sequence). You can calculate individual simple traits, but not, like, from first principles; those things only work for an organism you’ve already studied really, really well, and it doesn’t work for all possible traits. So since the models are imperfect, there’s still been room for continual improvement.

Besides: development is an ongoing process. Since it takes place over a lifetime, there are other factors involved in phenotype other than just the genotype. These factors are often described as “environmental”, things like nutrition… although note that your prenatal environment, impacted heavily by mom’s genes, will also impact your own development. That’s already very important for humans, but it’s even more important for plants since we are designing them to yield food, fiber, etc. under particular climatic conditions.