If a female has XX chromosomes and a male has XY chromosomes, what chromosomes do transgenders have?
10.06.2025 10:02
The single thing that determines sex is the presence of a gene called SRY. Its discovery in 1990 changed everything we thought we knew about sex in humans. And the biology of sex in humans is actually quite complex and occasionally quite messy.
So when you try to point to the absolute cause of “biological sex” — you can’t.
So before you hate on people for how they define themselves and wish to be known — what do you know of *your* chromosomes and genetics? One of the reasons there’s no genetic testing in elite sports is that every time it’s tried, a few people get really upset when their actual genetics don’t match what’s on their birth cert.
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If you are XY with a defective SRY gene — or one that’s blocked or your tissue is insensitive to androgens, you’ll have a female body, male chromosomes, and be genetically male. In some variations you might even be able to bear children, and in others you will be infertile altogether.
And that’s not even taking account of variations in karyotype sex such as XXY, XXXY, and XYY. (And yes, “karyotype sex” is the proper technical term for this.)
It’s the SRY gene that is responsible for the cascade of things that begin transforming the scrap of embryonic tissue called the “bipotential primordium” into male reproductive anatomy and the neurology to run it — what’s termed the *brain/body map* — starting at 5–6 weeks gestation.
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And while *gender* is a social construct, there IS a biological basis to our felt-sense of where we belong on the gender mosaic. That much is clear from decades of neurological, epigenetic, and endocrine studies. (Links to the studies upon request.)
If your X chromosome has an SRY gene, you’ll be physically male, chromosomally female (XX), and genetically male (SRY). And your brain/body map is likely to be *female*, in spite of having a penis.
But chromosomes do not determine sex or gender.
All this means you may be genetically male or female, chromosomally male or female, hormonally male/female/non-binary, with cells that may or may not hear the male/female/non-binary signal of your hormones, and all this leading to a body that can be male/non-binary/female.
Transgender people can have XX or XY chromosomes. They can also have XXY, XXXY, or XYY chromosomes. They can also have 46,XY in some cells and 46,XX in other cells, or 46,XXY.
So sex in humans is not binary. You can’t have a binary classification system if there are *any* variations, regardless of how few they may be — and the percentage of chromosomally/ genetically/neurologically intersex people may be as high as 1%.
So you can be XY — a chromosomal male — but have no SRY gene. You’ll have a *female body* and you’ll be chromosomally male but genetically female (because no SRY gene). And you’ll have a female brain/body map and there’s nothing in your felt-identity telling you that you’re not female.
In the absence of the SRY gene, all sexual development defaults to female — including the brain/body map.
The SRY is usually found at the tip of the Y chromosome (which is why science thought chromosomes determined sex). But it can be defective. Or, its action can be blocked by other genes (notably a mutation on chromosome 17 called CBX2). Or it can end up on the X because of a defect in that batch of dad’s jizz. Or it can be missing altogether.
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And your interoception (a neuroscience term) of your sex can be different from the evidence of your physical anatomy.
But there are a number of plot twists possible.
Hope that helps.