[Empire_of_Liberty]

This is your area of expertise, and not mine, but why wouldn’t dominant genes be “better”?

They’re more likely to be expressed, so they better be of some survival benefit to the organism. I would imagine that gene dominance is not something that is cast in stone, either.

[allmendream]

Both copies are usually being expressed under the same conditions; i.e. the gene is being transcribed into mRNA and then translated into a protein. But I imagine that by “expressed” you mean that it has the ‘dominant’ effect on the phenotype (what it looks like).

Huntington's disease is a dominant trait. It is not a “better” allele than a non-Huntington allele. It is “dominant” in that it only takes one bad copy stacking up in your brain cells and eventually driving you mad and killing you.

Brown eyes are not “better” than blue eyes - but the gene that says “put a lot of brown (melanin) in there” is dominant to the gene that says “don't put that much brown in there”. It is as if you instruct one worker to make a hill and the other to only fill in a hole- the one who fills it up “dominates” over the one who doesn't in that you end up with a hill. He isn't a “better” worker - both followed instructions.

Sometimes a bad copy is recessive in that it doesn't function - but one good copy does the job plenty well. In that case the “dominant” gene is better - but for every example of that there is a contrary example where it only takes one bad copy to mess something up!

If by “cast in stone” you mean determined by the molecular biology of the genes and the proteins they code for - then yes - it is cast in stone.

If by “cast in stone” you mean for every example where a dominant allele is better than the recessive allele there is probably an example where a recessive allele is better than a dominant allele; or neither is objectively better than the other - then no - it is NOT “cast in stone”.