heterozygote

Would they be fit, or are the heterozygote advantages for some genes too strong?

This fact worries me since I am an ApoE4 heterozygote and so the fact that it works for me may mean I have something wrong :/

The real reason is that these genes sit on the x chromosome, which makes it possible for women to be heterozygotes.

It also happens that heterozygotes of TD have higher myelin density.

I only skimmed the article, but it's always been my understanding that apple trees are extreme heterozygotes and that a seed from any given apple can produce a wholly new varietal.

Which lectures did you attend to learn about things like "net fitness advantage", "mutation load situations", "frequency-dependent selection", "heterozygote advantage".

Unlike the Fugate family's hemoglobinopathy, which likely did not provide any benefit, these two do provide some benefit to heterozygotes, and thus end up existing at a steady state in the population.

This is because seedling apples are an example of "extreme heterozygotes", in that rather than inheriting genes from their parents to create a new apple with parental characteristics, they are instead significantly different from their parents, perhaps to compete with the many pests.

But if intelligence is only worthwhile up to a certain point and it is controlled by frequency-dependent selection, or there is heterozygote advantage, or if intelligence is not necessarily reproductively fit at all, or other situations, then there could certainly be rare variants of large positive effect.