Quote from: Deinewelt on June 17, 2015, 10:52:10 PM
Well for one thing, the X chromosome is essentially the common base genetic material that all humans, male and female, share. This is why I always disagree with the whole argument that AMAB can not transition to female because, AFAIK, most, if not all, secondary sex characteristics are determined by hormones. Because this is true, the Y chromosome mostly effects the body through hormone production that essentially trigger other Y chromosome genes in the body. By modifying the hormones, you are shutting down those triggers and the resulting human form is, in my opinion, completely female.
Yep, contrary to popular belief, the sex you develop as isn't determined by whether you have a Y chromosome or not, but by what hormones are present during the time your prenatal development is taking place. As far as I've been able to find out, the Y chromosome doesn't do anything apart from direct your undifferentiated gonadal tissue to turn into testicular tissue. It contains far fewer genes than any other chromosome, and most of them appear to code for proteins associated with spermatogenesis. Since XY women are, on average, slightly taller than XX women and XX men are, on average, slightly shorter than XY men, it's thought there might be a gene on the Y chromosome that increases growth, but apart from that, it doesn't appear to do anything at all, except in gonadal tissue. All the non-gonadal cells in your body take their cue as to whether they're part of a male body or a female one from what hormones are present (which is why trans HRT works so successfully!).
There are a couple of differences to the way hormones work in adults and in an unborn baby though. In adults, androgens (primarily testosterone and DHT) drive male gene expression, and make cells behave as if they're male, whereas estrogens and progesterone drive female gene expression (which is why, in MTF HRT, antiandrogens on their own don't cause much in the way of feminization). In an unborn baby, androgens drive male development, whereas in the absence of androgens, female development occurs instead (in conditions where the fetus has neither testicles nor ovaries, such as Swyers syndrome or Turners syndrome, development occurs as female).
The second difference is that, in adults, hormones are largely concerned with directing various aspects of the day to day running of your body, so their effects are largely temporary. In an unborn baby, they determine whether you develop as male or female, so their effects are permanent, and stay with you for the rest of your life. Any disruption to your hormones during the time your prenatal development is taking place runs the risk of causing you to partly develop as the opposite sex to your biological one. This is why I think it's a really bad idea to be giving pregnant women medical treatment involving hormones. As the DES experience shows, one outcome is that you can end up transgender.
