Again, you seem to be conflating gender with sex which is incorrect. Sex is the correct term for a person’s physical traits and gender refers to a variety of other factors that relate to how that person acts. It’s helpful to look at it as being four seperate but inter-relating factors:

Biological sex — objectively measurable physical traits such as sex organs, hormone levels, and so on.

Gender identity — how a person thinks of themselves with regards to their gender

Gender expression — how a person chooses to display and ‘perform’ their gender

Sexual orientation — who that person is attracted to.

The above is a summary of a really neat diagram which I you can check out (http://itspronouncedmetrosexual.com/2012/01/the-genderbread-person/#sthash.naTj8x3M.dpbs ) if you want.