Heterosexual attraction in rebirth process?

In his book "Tibetan Buddhism from the ground up", Alan Wallace describes a part of the (human) rebirth process as follows: >"In [this vision] one sees (...) [the parents-to-be] in the act of sexual intercourse (...) and the bardo being is lustfully drawn to this event. Moreover, Buddhism says, this lust is directed toward the parent of the opposite sex of that being which is about to be conceived." I have some questions about this: - Is this the usual Buddhist view? If yes: What's the original source? - Do I understand it correctly that "lustfully drawn to" means sexual attraction? - If heterosexual attraction is a fundamental part of the human rebirth, how is this process supposed to work for homo- or asexual people?