My MIL does the same thing in a nice way...My FIL was one of 5 B I G and so of course I got the whole, boys just run in the family thing, but the fact is, the 3 men from that family who had kids ALL had pigeon pairs, and all those cousins had pigeon pairs, except for us. If it WAS genetics, it would have to be pretty selective that my husband was the only one in the whole lot of them that managed to inherit the "boy gene". I've finally convinced them of that but maybe I've just convinced them that it's better not to discuss the subject with me LOL.
I've studied heredity a lot while I was gone from IG and it seems really super unlikely to me that there are "boy genes" or "girl genes" that cause a family to have more of one gender than another, and here's why. Until very recently, most people (and animal species) lived in pretty isolated communities without a lot of interaction from the outside world. If such a gene had evolved, it would spread like wildfire as more and more of one gender would be born with each subsequent generation...even if it was balanced by a gene for the opposite gender, you'd see communities where one gene was more successful than the other, with way more males born and vice versa. But all around the world, in animal communities and human alike, the ratio is pretty close to 50-50, with very little variation either way.
To illustrate this, it's been proven that more males are born just after wars, if there really was a "gene" the first time there was a war and most of the males died, the females, who would be statistically more likely to carry "girl" genes (even if only men express those genes), would then produce kids with more and more "girl" genes and within a couple of generations, the community would be highly girl heavy. But instead, more boys are born instead - how would that be even possible if gender was genetically predetermined??
That indicates to me that while there are genes that might make an individual person more likely to be socially dominant, carry more muscle mass, and have a higher sperm count (all of which tend to produce more sons overall), these things are highly affected by environment, so if you lose social standing, lose muscle mass due to aging or changes in diet, or sperm count drops from environmental factors or aging, a person who once was likelier to have sons will then be likelier to have daughters. Gender ratio varies according to environment rather than being genetically determined, if it didn't, the human race would have died out a long time ago.