Liberals tend to believe that sexual orientation is determined by genetics but that gender-difference in behavior is not, whereas conservatives tend to believe the reverse. But, of course, as we see here these are related issues.
While I'm not the duly-appointed keeper of the Book Of What Liberals Think, I don't really think this is an accurate characterization (or caricature). I think the liberal position is that a lot of perceived gender-based behavior differences have strong cultural roots and reinforcement, and that even the perceptions of differences, which are not always correct, are strongly culturally defined. While men and women are clearly different in some sense, there isn't really evidence out there to prove that many of the stereotypical "differences" (girls are bad at math!) have a genetic or biological basis.
Most of all liberals understand that the effort to pin it on genetics is part of a movement to convince the world that the lack of proper female representation at higher levels of power and success is just "natural" and therefore nothing we should worry our pretty heads about. But that's not the same as thinking that no differences with genetic roots could exist.