Not you/Like you continuation

In Not you/ Like you, she sort of touches on biologics. She says "That at heart X must be X and Y must be Y and X cannot be Y." This reminded me of "The egg and the sperm: How science constructed a romance." Because each gender has it's chromosome. I think she is saying sarcastically that if you think other wise you end up in rehabilitation or a mental institution because thinking otherwise must be implausible! I believe what she is trying to say, once you look inside of your self you could be X, or Y or even possibly be X on the inside if your Y on the outside or vice a versa. This reminds me of what we touched on in class and how those who are transgendered must feel being trapped in the gender that you feel doesn't belong to you.