Thread by @delaneykingrox

1) why you can't class humans into two categories by genitals. Some science.

2) a glance between a newborn's legs is a pretty good indicator of their sex. However, it isn't a foolproof method, and here, in simplified terms, is why.

3) you all know the egg and sperm sitch. A sperm gets into the egg and that good old magic happens that results in a future taxpaying voter.
The deal is you get half the dna of your egg and half from the sperm. Switcharoo presto, and you got a new sequence of DNA. Noice.

4) a chromosome is a packet of DNA, and when it comes to sex, you probably where taught that the X and Y chromosome is how we get boys and girls. An X meets an X, you get a pink crib, an X meets a Y and you get a blue one. Right?

5) the sperm either has an x
X or a Y. So daddy picks the sex. (Someone tell Henry VIII)

But the problem is that is where our education usually stops.

6) let's go a bit deeper so you are a bit wiser.
The important part of the Y gene which makes it chocked full of manly goodness is called the SRY region. Infact it appears to be the only important part in deciding sex.

It's basically the order form for a boy. Nothing more.

7) the rest of your DNA contains information to make both a boy you and a girl you. By default, the boy stuff is basically switched off. Like dip switches on a computer.

8) if you have the SRY region, that kicks off a chain reaction the *usually* results in cheaper haircuts and better wages... aka, manhood.

But not always.

9) the important thing to understand is the chain reaction. I need to set some ground work first.

Ovaries and testes both form from the undifferentiated gonad. No SRY? Ovaries. SRY? Usually testes.

Let's say the tested form as usual, they will start making androgens.

10) androgens are hormones such as testosterone and dihydrotestosterone (which makes you bald btw).

The growing fetus emits two baths of androgens during two stages of its development.

So what does it do?

11) well, here's the thing. As I said, your dnd has both sets of instructions- male and female. Our cells actually don't give a crap which set they use, they just go with the one they have activated.

How is that DNA activated? By hormones. Specifically here, androgens.

13) cells have androgen receptors on the surface. Androgens snap to that shit like a key to a lock. Once that happens the receptor enters the nucleus of the cell and does a sort of tumbler thingy to your DNA, turning some bits on and some off.

14) the cell then does it's thing, eventually dividing and the process continues... bind, activate/deactivate DNA... do whatever the cell does and divide...etc etc.

So you start developing sex characteristics based on whatever hormones you have AT THAT MOMENT

15) so this is where genitals form. Yay. Very handy.

Genitals all start as a bunch of ducts that slowly develop or self destruct depending on what hormones are around.

Are you starting to see what I mean?

16) The Mullerian duct, for example, grows up to be the upper third of the vagina, womb and fallopian tubes. If the hormone AMH is around, it withers away.

(Women who make AMH are missing their wombs.)

17) the clitoris and the penis develop from the same tissue. Take a good look at a clitoris and you will see it is very similar to a teeny penis head. If you get those androgen baths, the clitoris develops into a penis... sometimes big, sometimes very little... and here...

18) comes challenge number one... how big does a clitoris need to be to be classed as a penis? Hmm?

Okay lets aim down a bit.

The labia and the scrotum also start as the same tissue. The labia fold over and fuse, forming the sack... that's why scrotums have that little seam

19) the ovaries stay still or, if if androgens are about, begin being tugged down into the scrotum. Slam dunk. Nothing but net.

Except... you know sometime the labia don't entirely fuse. You get something that kinda sorta is a vulva... but kinda sorta not...

20) challenge two: is it a vulva or an open scrotum? Who gets to decide? And why?

If you want to know where the wee hole can end up in all this, google hypospadias.

21) see, all the way along this chain reaction, from egg meeting sperm, to cell division, to gonad formation to hormone reception that chain reaction can vary. Throw in cell mutation and chemical interference and wow, do you have a lot of variation.

22) humans develop over time, and are ridiculously complex. We are rich in variaton. There is no ideal or pure version of us. Not even twins are truely identical.

Humans do NOT come in male and female only, we are a constant shifting flux of cells and hormones.

23) shifting hormones before the brain develops (late 2nd early 3rd) may lead to a brain that develops towards one sex, wholst the genitals forked off in their own direction months before. Ie. Trans

If we do this to rats, you get male rats behaving as female rats.

24) some of us have androgen receptors that don't accept androgen. This is called CAIS and PAIS (complete and partial androgen insensitivity)

25) CAIS people have XY chromosomes, testes, androgens and end up classed as girls because they are born with vulvas

Their cells cannot lock onto androgen, so they default to using the female dna coding

26) partial androgen insensitivity results in a sort of mix and match as only some of the cells lack the ability to bind androgen.

27) some people classed at birth as women start producing testosterone due to non congenital hyperplasia, where an enzyme difference results in adrenal glands making testosterone

28) guavedoches are people who are assigned female at birth but start developing into male genitalia as puberty hits.

29) this chain reaction I have shown you means that the Trump administration's attempt to erase transgender people causes massive damage to a huge percentage of the population who do not fall neatly into male or female.

30) Science backs intersex, transgender and homosexuality as biological fact.

There is no shame in being born diverse. There is no crime in it.

The administration is ignorant, hateful men with no grasp on biology.

It fascist propaganda and denies the human right to exist

31) and if you are still not convinced, the Olympic committee would love to have a neat way to categorize by two sexes and have offered a LOT of money if you can solve it for them.

Good luck.

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And if you want to read more of me waffling on about this stuff...

https://twitter.com/delaneykingrox/status/995525175255879682?s=19