If you have a the SRY gene you're male, if you don't, you're female. It's that simple. It says nothing else about you. Even though sex and gender are strongly correlated, there's plenty of scientific evidence that suggests that being transgender is a legitimate condition and not something that people are making up. Interestingly enough, the studies determined this by looking at the brains of transgender individuals and comparing them against the areas that differ based on sex and found that in many ways a transgender person has a brain that looks more like the brain of the sex they feel like they should be than the brain of the sex that they are.