When conceived, there is either a joining of an XX (female) set of chromosomes or an XY (male) set of chromosomes - this is basic genetics 101. Even if a person is confused about their gender, they undergo hormone therapy and undergo radical surgery to alter external sex organs. If some 300 years from now, someone would come across the grave of a person who had taken hormone therapy all their life and had gender reassignment surgery; if they ran genetic testing on that skeleton that they had found 300 years later, they would say this person was male or female based on the residual effects of having XX or XY chromosome.
-Dr. Kirk Clayton
