Sexually antagonistic genetic variation, in a simple model, will persist if the benefit to one sex is (near) equal to the cost in the other, otherwise the polymorphism will be selected out of the population.

[Rice's theory][1] suggests that sexually antagonistic genetic variance should be over-represented on the X-chromosome, because males are hemizygous (thus express male beneficial alleles more often than females) and females have the X-chromosome 2/3rds of the time (thus female benefit does not need to equal male cost for persistence). This model expands the range of conditions under which SA variation can persist.

[Fry argues here][2] that unequal dominance means the conditions under which sexually antagonistic variation can be maintained in the autosomes. Because of dominance the mean population fitness is increased under conditions of polymorphism (cost of a new allele to one sex < the benefit to the other). This model also expands the range of conditions under which SA variation can persist.

I think Fry concludes that the X-chromosome should therefore be expected to, not only not be a hotspot, but to be a coldspot (a dearth of SA variation on the X).

Conceptually, why does the hypothesis of unequal dominance make the autosomes more permissive to genetic variation than the X-chromosome? (Therefore making the X- a coldspot for SA variation). This is what his abstract says, it seems to suggest that...

"..such polymorphisms are expected to be more common on the X-chromosome... here I show that there are plausible assumptions under which the reverse is expected to be true."


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