Never heard before that the weird chromosomal abnormality conditions can be passed on, I guess its so extremely rare and likely to cause sterility, so its not exactly a topic with a wide range of data to look at. Maybe its a guess that similar to other chromosomal damages like down syndrome, it can be passed on as well.

As for the gay thing, in theory a 'gay gene' would be hindering any and all propagation of that gene, so it may exist as an evolutionary quirk for a little while on some time-scale but would always self-eradicate. What instead supposedly has been found to exist is a gene that makes one really love the dick. When a man has this, he is gay(or likely to be), and that genetic condition becomes an evolutionary dead end. However when a woman has the gene, she is super-promiscuous and propagates the gene via her many babies. So there are sufficient conditions evolutionary speaking for this gene to persist somewhat since it makes the positive of the woman balance out the negative from the man.