From a purely anatomic point of view, one's gender is determined at conception; if the mother's egg is fertilized by a sperm with a Y chromosome the fetus is genetically male (XY) while a sperm with an X chromosome will produce a female fetus (XX). Anatomic differentiation of the fetus' genitalia is evident by 6 weeks and secondary sexual characteristics develop at puberty; however, a variety of chromosomal, hormonal and genetic abnormalities may interfere with this process, leading to ambiguous genitalia in approximately 1 of 4500 births.
Increasing scientific evidence suggests that an individual's sexual orientation and gender identity are also genetically determined, involving genes that are distinct from those directly related to anatomic gender. Recent DNA studies involving identical twins indicate that genes on Chromosomes X and 8 may play a role in homosexuality while studies in animal models have demonstrated the presence of many hormone-sensitive genes that might determine gender identification (i.e. these genes may have increased or diminished sensitivity to pituitary and gonadal signaling).
Clearly, based on social observations, one's anatomic gender, sexual orientation and gender identity are independent traits; the great majority of homosexuals identify with their own anatomic gender while transexuals, whether homosexual or heterosexual, identify with the opposite gender. While definitive evidence of a genetic basis for sexual orientation and gender identity currently remains elusive, we do a disservice to members of the LGBT community by denying the complex nature of human sexuality. In time, despite the self-righteous proclamations of religious zealots, science will provide the answer.
