Well... gender is internal. Sex is external. (or at least that's what the definitions seem to be changing to... and the ones I use).
If we could change gender, change my brain, I would have done it in a heart beat. But we can't... so I gotta change my sex the best I can. Hormones, surgeries, etc. Still gonna be missing a few internal parts... still gonna have those chromosomes... but gotta work with what I've got...