The Mirrored Road into the Interior

SO, last year I read Wen Spencer's A Brother's Price . Base premise is an alternate earth where male births happen less than 1/10th as often as female births, and thus men are very much disenfranchised.
I like the story, I like the setting, but for the past year, a couple things have been nagging at me.

One, I want to know the mechanism for this culling.
There are textual hints that it originates with the men, specifically that some men ten to sire more male children than others, but this could very well be on the level of folk lore. Further more, I'd want to know if this was genetic (and if it is, how it is maintained. Imbalances on that scale tend to even themselves out in most populations quite quickly, and her humans aren't different enough behaviorally or socially to counter the selective pressure toward a 50/50 mix. In fact, their society seems to be set up to encourage it, putting a strong value on males who sire male children. With the extremely large brood numbers within a single family and the tendency to sell off male children, even small increases in the number of male children in a family would spread throughout a region in a hand full of generations.) It can't be a recessive X linked trait or there would be people out there with normal splits of male and female progeny, or even a co dominant x-linked (like ss anemia if it was on the X. Only female double carriers and male carriers would die of it. Wait, you'd never get female double carriers since male carriers are never born. Or it would only be with errors in the production of germ cells. Assume an Xx female and an xy male, Xy don't make it to term. so 1/3 of the total offspring carry the X gene with a tendency to half as many boy children as girls. In the next generation, the girls who have the xx gene set would tend to have more offspring than their sisters with the Xx set, if for no other reason than that they'll have fewer misscarrages, by about a quarter. Very quickly, the doubled effects of 1/4th again as many children, twice as many boys, and2.3s of even a carrier's children not being carriers, would make the X gene uncommon) and we would see those families grow very quickly. Oops more later. I'll get to my arguement for sperm banks shortly.