Gender is a state of mind. Re-read that. Again. I want it engraved on your brain cavity. Some, or many, confuse
gender with
sex.
Sex is a physical state met by a broad simple requirement, or several intricate requirements. Sex implies one of two statuses based upon the type of genitals one happens to be endowed with at the time. Sex also implies that certain
chemicals, reactions of said
chemicals, and
physical responses to said reaction are all present within the body of the person in question, some only in the case of
arousal or adjacent to the
act of sex.
All those technicalities stated, gender is none of that. Gender is the mental state of being affiliated with one of the two physical sexes. In the case of most people, Gender and sex line up, hence the confusion about those who don't. However, in some cases, the two get crossed up. Some are born female, but feel (meaning they mentally affiliate as) male. This is something that really cannot be helped. Gender cannot be forced to change without serious mental trauma, although physical sex can. This leads to a fairly simple conclusion, which is to physically switch sex. The complications of that, being easier said than done, is enough to fill more nodes than I care to write.
The question then comes as to what one could identify as association with the opposite sex. The answer is varied and cannot be explicitly stated to fit every example. Simply put, you just figure it out, it's different for everyone. Whether it's an emotional trigger of realizing you want to be more effeminate than a male feasibly can, or a psychological one of understanding you've always been on the wrong side of the fence, or even a raw sexual urge to become what you were genetically programmed to mate with, any reason that would make you genuinely consider the process of a sex change is, by and large, going to be a valid one, given that you fully understand what such an operation entails.
While many, including myself, cannot fully comprehend what it means to be locked out of what is the sex that matches to your gender, it can be understood that an uprooting of something so basic to our natures would be immensely difficult to deal with psychologically and emotionally. When a person is going through that, they cannot be as steadfast in their gender-sex association as those who match naturally. What those who do match from birth must realize is that those who do not are not strange. They aren't odd. They are humans, and they had a mix up at the factory, and while they're working to fix it, the parts need to be ordered and will take sometime to arrive. Until then, they must cope with change, and treating them different is a horrible thing to do. That is to say, if they state they are female, in gender but not sex, treat them as female. Not because they say they're female, but because she is. She's a girl, plain and simple.
Please note, this is not meant to be an indepth discussion about sex and gender. This is an examination of the surface. I'm aware of the multiple sexes and genders outside of the "standard set" so to speak.