It depends on who you ask..
Some people will just go with the "Well...look at them! It is not that hard to see who is what."
Those are the same people that believe homosexuals will burn in hell.
Then others will say "It is all a matter of the genetics! XY or XX. Simple."
This makes sense, but in this day and age simply brining it down to a science simply does work.
If you ask me...it is somewhere between those two yet at the same time neither.
A lot of it seems to reside in the mind of each individual. There are some people out there who truly believe that they were born into the wrong gender, and find themselves attracted to the same genetic gender. These same people sometimes go through with sex changes, which then makes them transexuals.
Ofcourse, everything is based off of old notions and words meant to define and classify. Yet when it comes to living, breathing people does it seem right to just classify and define then based on a word?