I think you are wrong. When I took biology, the word gender was never used. I heard it a lot in Spanish class, though.
Oddly, in my French and my biology studies, we used pretty much the same terminology. In zoology, we had to determine whether every single specimen was male or female. And in French, we had to learn which words were male and which were female. As I recall, whenever we were talking about sex in biology, it was very much in the reproductive sense. And that is the way I use the word. Except that I prefer euphemisms.