Actually, i think there is some merit to looking at the body (sex) as a physical expression of gender.
The body doesn't always match the gender identity, which sucks for trans people. But it is sexual expression, ie how the cells of the body are expressing features based either on the current hormonal balance, or the hormonal balance during some part of development.
So you get gender identity, body expression, gender expression. As three parts of the one thing. You can try to alter the body or your clothing (butch, femme, androgynous, neutral, hyper-masculine)
We currently have no methods which alter gender identity. It appears to be hard coded in the brain during development. Likewise with sexuality is hard coded. You can even read testimonies of people who have converted from trans/gay lifestyles for religious reasons, and they say how they are tempted every day, but resist.
As if they have not changed who the are (either gender identity, or sexuality) But they have changed their expression.
I fear this is a horrible thing to encourage someone to choose, but i also feel i should respect their rights to choose it. (just like my feelings on breast augmentation for cis-women who feel it will improve their self-esteem - i think a culture which encourages young women to have themselves cut open is messed up, but until we end that culture i support their right to make that choice)