Just as a reaction and addition to the comment Colleen started.
I too have observed guys teaching more often than girls. In my observation they are often telling/teaching it wrong anyway, so they better shut up and train, but it probably takes a lot of experience to realize that.
I have also observed some other things that might be related to this isue. Note that these are just observations I made in class and are not ment as generalizations.
[*]People often ask a guy for advise, even when a more experienced girl is closer.
[*]The word/advise of a guy is better. (I have even encountered situations where the same advise as given before by one of our female sempai was accepted when sensei or one of the male sempai repeated it)
[*]People confuse physical size with experience. (I have seen absolute beginners ridicule the advise they got from on of our very small female sempai because the thought a small girl good be no good anyway. The same thing happens sometimes with people judging ukemi, ukemi done by a very big male is considered to be better and more spectacular then the same ukemi done by a small female).
[*]Girls tend to ask more, wanting more to be guided through the technique/exercise. (Yes some girls give me blisters on my ears from asking, unfortunately some guys do the same thing trying to explain something to me)
[*]Guys seem to work from the notion that they are doing it right. Girls seem to work from the notion that they are doing it wrong. (Guys often ask things like "this was good wasnt it" as where girls seem to ask "what am I doing wrong", often in situations where the questions arent important anyway.)
[*]A lot of the girls in class have no desire to act like the dominant male in the group. (Funny thing is that the ones that do leave our club and join a different almost all male club nearby, go figure)
Just some observations.