http://vector.tutsplus.com/tutorials/the-differences-between-male-and-female-portraits/

It is hard to compare male to female faces simply because each face is unique, but there are some features in the face that can make a male portrait look more masculine or a female portrait look more feminine. In this article we’re going to take a look at those features. You will be able to accentuate your drawing in those regions, so that the masculinity or femininity will become more prominent in the portrait.