Beachcomber, I genuinely think it's down to how one chooses to identify oneself. It might not be 'true' but then 'truth' vis--vis identity - isn't that the kind of monolithic concept we wanted to, if not get rid of, at least interrogate?
ICan, not knowing much about teaching biology, I don't know how I'd teach a trans-friendly biology lesson. But there is of course physical biology, which is, at the end of the day, what it is - plain for all to see. But then there's subjectivity, which isn't static, IMO.