I understand there is a debate within the gay community as to whether gays are born as gay, or if it's a choice ("sexual orientation" -v- "sexual preference"). I would think it's a combination; like with intellect, it's a combination of what your genes provide, and the environment in which you live. (Someone born "retarded" could never become a doctor; and someone born very very smart, if they're never exposed to learning and education will also never become a doctor (western MD).
Being trans is, imho, largely a function of the brain being changed, either by hormones in the womb, or by emotional trauma in life (and perhaps other things, too). But I wouldn't think a "person" is defined by their genetics.
But, I'm no authority. Believe what you will, harm none.