Intersex

You have not described a person with CAIS here.

Those with CAIS have no uterus, cervix or fallopian tubes.

No, it includes those with PAIS, of which all are women. If you added PCOS on top, the number would be much higher.

The figures are around 0.2% if you remove women with PAIS, and 0.0018% are conditions that result in ambiguous genitalia.

What do you mean what would happen to them? Hopefully they'd be left to live their life in peace?

Sex is determined at conception. There is no default sex.

People erroneously believe this because early foetal gonad development resembles a female phenotype.

It's only 1.7% if you include women with pcos

"Yes, you can be a male or a female with a DSD - I agree with that. And intersex is a misnomer in that sense".

You ARE a male or female, even if you have a DSD. DSDs are specific to sex. There is nothing in between. No third sex.

Well yes it is 100% due to their chromosomes or more specifically their genes on all 23 pairs (plus or minus any additional/missing). It’s not just whether they are XX XY or any other combination of that chromosome pair - eg 5ARD is XY with presumably a gene elsewhere that means the relevant parts of their body are resistant to androgens so develop along a more externally visible female path. Still a man with a male DSD.

in your hypothetical cheek swab situation - most people will look exactly how you would expect given their XX/XY swab. Anyone who doesn’t visibly/medically match (eg XY CAIS) will have further investigation to identify the exact DSD. There is then a decision to be made by someone (not sure who) as to whether these would be classified as male or female. Medically an XY CAIS still has to be screened for prostate not ovarian cancer, but in day to day life would be female.

focussing on these edge cases is not a good reason to say that a cheek swab is pointless for 99.9+% of people/situations.

Foetuses are not female by default. Sex is determined at conception.

Put simply, a Y chromosome probably gives you greater strength etc?

There are some incredibly rare conditions that do not fit into XX / XY. As they are discovered they are surprising drs because it really isn't that simple, and because they are so rare they often only come to light when professional sport is involved (you wouldn't know in everyday life)

I think where situations are segregated by biological sex, those who have dsd need to be considered on an individual basis, that said it is rare so on most situations it is pure theoretical.

Not chromosomes, but specific genes within chromosomes.

Your scenario rests on the premise that humans have a total understanding of the human genome. Which we do not.

The discovery of the SRY gene was a massive step in our understanding. But it's not the whole picture. Since then, various other genes have been found to play a part in sex determination.

Even with the incomplete picture we have now, a simple cheek swab would give you a person's sex.

On top of that you have the sociological argument of how we categorise those with certain conditions. This is most clearly shown in the discussion around those with CAIS, who are biologically male, but are generally accepted as female, given the fact thay cannot process androgens.

For the 0.018% of the population with DSDs it is slightly more complicated but they are still male or female. XX and XY works for 99.9% of people

Very interesting. Though we are getting dangerously close to admitting that biology of phenotype is much more complicated than xx and xy!

I saw a talk by Prof Robert Winston and I believe that he said if you have an SRY gene you are male. SRY genes are usually found on the Y chromosome but in some DSDs it may not be. I think he also added functional testosterone receptors as a condition for being male - this would mean that he would classify people with CAIS as female

A very small minority, obviously.

Sorry, trying to do three things at once.

That’d be you, it seems?

Everyone would have a birth certificate stating their sex, issued after their sex had been verified possibly during gestation and certainly at birth, either through observation (the vast, vast majority) or through further tests and investigations if necessary (a very small majority).

Official ID documents such as driving licences and passports would show the same sex.

No-one would be allowed to falsify their official ID.

Very simple.