Sex Determination in Humans NOT SUS
Yes, this is relevant to USABO. Trust.
This article discusses sex determination in humans; in other words, how signaling pathways decide your biological sex when you're in the womb. The processes of sex determination begin after around 6 weeks of pregnancy. Chromosomally, females are XX and males are XY (ignoring aneuploidies). The Y chromosome contains the SRY (sex-determining region Y) gene, which codes for the SRY protein. This protein is a transcription factor for genes promoting testicular development. Notice that, by the construction of this system, everyone is female by default unless they have the SRY apparatus promoting development of male anatomy.
But let's back up a little and talk about anatomy. Close to but before the 6-week mark when sex differentiation begins, babies have both Müllerian and Wolffian ducts (these are not gonad precursors; they will differentiate to become non-gonad reproductive structures like the uterus or vas deferens or something). Prior to differentiation, the gonads are bipotential gonads - they can either become testes or ovaries. If the aforementioned SRY thing doesn't happen, the Müllerian ducts will mature into female anatomy. If the SRY thing happens, the Wolffian ducts develop into male anatomy.
I have a stupid mnemonic for this. I remember that the singer Mae Muller (listen to Anticlimax, Therapist, and the song with Polo G I forgot what it's called) is a woman. Also, I remember Adam Levine, a man, making that weird wolf sound in Animals before the beat drops.
Ok anyways. Here's what the ducts look like prior to maturation:
Random aside: notice the rudimentary cloaca, a common opening for urinary and reproductive waste. It's kinda like birds, which also have cloacas that release poo and pee from the same hole (that's why bird droppings have white stuff and black stuff; that's the uric acid and poo, respectively). Birds also rub their cloacas together for sussy activities...
Anyways, from this undifferentiated stage, sex differentiation occurs. There's a hormone system controlling this.
So in a male, after the SRY protein promotes gene expression to turn bipotential gonads into testes, the testes make testosterone to promote differentiation of the Wolffian duct into the non-gonad male structures like the vas deferens, seminal vesicle, etc.
Remember the thing about “female” being the default setting? Here's where that becomes relevant. The absence of SRY stuff promotes female anatomy development.
This raises the question: if "female" is the default setting, what stops males from developing not only male, but also female anatomy? The answer lies in another hormone made by testes: antimüllerian hormone/müllerian-inhibiting substance (MIS). This prevents development of female anatomy when testes are present.
Here's a flowchart of the whole process:
Yeah that's it. Here's some stuff:
https://youtu.be/ciQjo7bj-uQ - helpful video on this topic.
https://byjus.com/biology/difference-between-mullerian-duct-and-wolffian-duct/ - some fancy terms on this topic.
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