Yeah. Your chromosomes determine your "physical" gender. Basically, you're either XX (female) or XY (male). While some Hermaphrodites do exist (containing elements of both XX and XY), they are extremely rare. Having the desire to have sex with members of the same gender, obviously stems from one's mental choice and thinking you are opposite the actual gender that biology gave you is still just in the mind which is not the same as one's actual gender. Ultimately, it boils down to the physical reality versus the mental image of one's self, however, insisting that someone who firmly stands with the biological status of genders, must compromise their reality with another person's personal belief as to who they are, is asking them to basically "pretend" you are what you claim you are and many won't do that.