Suppose it is genetic ...
If it is genetic, how is the trans gene passed on. If you don't marry and have kids, the TG gene doesn't get passed on. To the extent that that's true, being TG should die out.
Another thought question, how many TGs have TG offspring? Even two or three generations away?
Probably not, but who knows, and who cares?
First of all, most CDs, according to surveys, are heterosexual (married heterosexual, to boot). That means if being TG is genetic, the TG "gene" will be passed on.
Second, if being gay was genetic, then in theory it would not be passed on. Of course that neglects that sexual preference does not prohibit sexual reproduction.
In the end, I have no idea why I wanted to put on a dress when I was a young boy. It doesn't really matter whether I inherited it or learned it (the classic "nature versus nuture" debate), I just know it's something that has always been a part of me.