They will tell you that gender and sex are two different things. Don't fall for it.
"Sex" has referred to your gender (male and female) in all cultures in all the world throughout the history of human existence. It doesn't change just because a small group of people change the definition and the meaning of the word. Sex refers to your gender and always has.
"'Sex" is what's between your legs and 'gender' is what's between your ears" (what you believe you are instead of what you actually are).