Satinavian said:
If sex is the biological thing and gender just some social construct, i fail to see how medical professionals qualify for gender questions at all.
So, there's a third layer between the biological and the social, isn't there, and it has its own discipline.
Biology looks at the physical structure and operation of living organisms.
Sociology looks at the way in which individuals interact together as a society.
But between the two, there is a science which examines the workings of the human mind. It's called psychology, and it's quite important in medicine because we understand that health issues are sometimes due to the way the mind works, rather than just problems with the body. It's from psychology that we get the separate concepts of gender identity, sexual orientation and, ultimately, gender expression.
We don't currently know what prompts a person to develop gender identity. It may be partly to do with sex hormones, or it may just be a very complex cognitive process which takes place at a very early age. What we do know is that it isn't a neurosis or delusion, it doesn't work like one. It is a seemingly natural variation on the way in which all human beings come to develop identity which, in a society with very rigid gender rules, has unfortunate and tragic implications for the individual whose gender identity does not conform (this is the part sociologists are interested in, but their interest is more theoretical and less clinical).
We are born physically with particular sets of organs, but we are not born with an identity. As we develop from screaming babies into human beings with complex thoughts and language, at some point we develop this thing called identity, a sense of who we are, which is very important to us. Most people come to identify strongly with the sex they were assigned at birth, but some people do not. The very existence of those people already demonstrates that gender (gender identity in this case) is not determined by "chromosomes".
Heck, "chromosomes" on their own don't actually do anything. The importance of the Y chromosome is that it normally contains the gene that triggers testis development in humans, and because it's much easier to see chromosomes than individual genes we use the appearance of the Y chromosome as a kind of rough way to estimate the presence of this gene. However, it's not a very good test. At one point, it was common to karyotype test athletes, but we stopped doing that because it's not accurate enough at determining a person's sex when compared to actual medical examination.