Could someone explain what the y and x chromosome are, what part they play in our biology and how they determine our sex? I hear this topic come up a lot and I have no idea what they are. Doesn’t an extra chromosome also mean a person might have down syndrome? Thanks guys.
(Not looking for a political debate btw, just straight biology, thank you)
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The chromosomes are just certain settings in a big long string of DNA. Those settings determine what proteins are produced, in what order, and by a very complex process every time a cell splits it is determining how that cell operates, what type of cell is made, and what other proteins are produced.
Those settings literally determine almost everything that every cell in your body does, including how to make those cells and how each of those cells is different in your eye, your brain, your lung, your blood or wherever.
When that cell is an egg cell and a sperm cell and they mix their DNA, that determines the “sex chromosome” of the child.
However, the sex chromosomes are far from being the only determiner of sex, by the way:
[https://twitter.com/RebeccaRHelm/status/1207834357639139328](https://twitter.com/RebeccaRHelm/status/1207834357639139328)
There’s no such thing as “XX is always female”. That’s literally nonsense. And why 1% of people are medically “intersex” and many of those that aren’t intersex actually have entirely the “wrong” sex chromosome for their outward-facing sex. This is also the cause of some infertility – people who have every aspect outward-facing of being a female and have lived a perfectly ordinary female life for their entire existence actually have male sex chromosomes that just aren’t being acted upon, so they have trouble conceiving.
Also: It’s not true that there are “only two options” even when it comes down to pure chromosomes. The same way you describe Down’s as being an extra chromosome – that can happen just the same for sex with someone ending up with an XXY chromosome, for example.
Depending where such “errors” occur in the DNA, they can result in Down’s and significant developmental problems, or in the sex chromosomes and thus result in all kinds of effects on your body, genitals, hormones, fertility, etc.
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