So, a woman inherits some nasty genetic defect that blocks production of some key protein. What happens? Typically little or nothing, because that defect is only expressed in 50% of her cells. Most of the time, the same is true for us men.
However, if the defect is on the X chromosome, of which (most) women have two copies, but (most) men only have one, then the men who inherit it will typically die, if they even make it to term, while the women will live And (most) women do not have a Y chromosome at all, so they will never see a defect on that chromosome.
My point? Is life unfair? Not. Turns out there's a reason operating here. You really don't need all that many men... In a typical primitive tribe of the kind that our ancestors lived in for a few million years or so, you only need enough men to fight off the wild beasts and the nasty neighbors. And, since most women died young of childbed fever or other complications of being continuously pregnant from 12 years old until death, you really needed some ways of dealing with the surplus men anyway.
So, the nasty bad mutant genes that wouldn't be expressed in women - or not to the same degree, would get eliminated altogether on the male side, by their early death. At the same time, women were scarce and at a premium, as they died anyway by their mid-thirties, so you wouldn't want to test new genes, good or bad, on the mothers, not when you've got all those useless extra males running around causing trouble. Thus, the males, as usual, are the genetic test beds. They take the risks, both behaviorally, and also genetically.
However, this only works if the new gene is on the X or Y chromosome. Otherwise, it hits women just as hard in most cases. Ideally, any new unknown variants of a gene would show up first on the Y chromosome, so that only men would be affected. Then, if it passed muster as an improvement, or at least not a serious flaw, via recombinations, the gene could drift over onto any of the other chromosomes, where both sexes would benefit.
Since this would be the ideal, the logical questions to ask are: Is this ideal realized in actual nature? And, if so, how? And, if we how how, then what implications are there for internal management of genes that might impact other areas?
Could there be a mechanism by which new genes are somehow recognized as such and systematically shunted to the X or Y chromosomes for testing? And, once a gene has made it there, is there a way that a kind of "aging" tag system could be employed by the cell to give it the seal of approval? This would certainly be nice, if the case.