I’m going to unpack some of this.
1. The premise that women are unknowingly carting around a Y (with SRY) is massively over exaggerated. The risk of Surprise SRY is minimal.
2. The risk of Surprise SRY is, however, non-zero. But in reproductively healthy women who have had periods and, more definitively, had kids is as near to zero as one can map in science.
3. That is, if you are a person who got a period before 16yo (ish), who has ever been pregnant or who has had the kind of screens that are offered to women (like cervical screening) without any drama, I’d bet my house you don’t have SRY.
4. If you have proof you have popped eggs and/or seen your ovaries, you would be almost singular (literally in the scientific record, the second case to my knowledge) if you also have SRY, functional or otherwise. If that’s me, with my entirely healthy reproductive system and physiology, I’m writing myself into a paper.
5. If you are born appearing female but actually carting around a Y with an SRY, it will almost always make it’s presence felt during puberty. You won’t menstruate, your GP might then discover unusual anatomy etc. Nobody in the U.K. should be getting Surprise SRY.
6. Ironically, Mums to boys are the most likely confounder (via fetal microchimerism). It should not need to be said that picking up some cells from the baby boy you’ve carried in your belly doesn’t change your sex. The carrying of the baby boy, almost certainly from your own egg, refutes that. 🙄
7. If, despite being an apparently healthy woman, you get a Surprise SRY, that means you’re an interesting woman, not a man. It also means that you won’t be excluded from female sport. Because whatever your genetics, sport is divided on bodies.
8. The lay person’s fascination with genetics and the cultural position that DSDs are “just normal variation” has led a fair amount of even normally-sensible people down a dumb rabbit hole. They are medical conditions that are really rare. 1/20k is a binned frequency that we use in genetics to describe things that are really rare. It’s not a measured number, it’s almost qualitative.
I reckon you should have every single TERF take this test themselves.
Be wonderful to see how many of them have a Y chromosome they've known nothing about their whole lives.