I don't want to claim to have more knowledge than you do. But to the extent that Dr. Dobson is trying to suggest that there is no possibility of genetic influence, I think that is mistaken. He is assuming that gays do not reproduce at all. But gay men do father children; the figure I have seen is that they have 20% as many children as heterosexuals. That's a lot fewer but far from zero.
That said, I think there is too much focus on genes rather than other biological factors. If this were my field of research I would looking at whether something that the fetus is exposed to in the womb might be influencing the developing brain in a way that influences masculinity/femininity and ultimately sexual preference.
They would have to be heterosexual to do that...
That is a biologically driven heterosexual desire.