The simple idea (no memorising)
Very early on, the embryo has a gonad that could become either a testis or an ovary. Doctors call it bipotential — "able to go two ways."
There is a gene on the Y chromosome called SRY (think: the Sex‑determining Region of Y). It is the switch.
- Switch ON (SRY present) → the gonad becomes a testis.
- Switch OFF (no SRY) → the gonad becomes an ovary.
What the testis does (so you understand the female path by contrast)
If a testis forms, it has two kinds of worker cells, each with one job:
| Cell | What it makes | What that does |
|---|---|---|
| Sertoli cell | AMH (Anti‑Müllerian Hormone) | tells the female ducts to shrink away |
| Leydig cell | testosterone | builds the male internal tubes; converted to DHT to build the outside |
So the male recipe is: make AMH to remove the female plumbing, and make testosterone to build the male plumbing.
The female path
With no SRY, none of that happens:
- no testis → no AMH → the female ducts are free to stay and grow;
- no Leydig testosterone → the male plumbing never forms.
The body quietly follows the female blueprint.
A better way to think (don't memorise "Y = male")
Instead of "Y chromosome equals male genitals," think in a chain: SRY → testis → (AMH + testosterone) → male body. Remove any link and the female pattern appears. This chain will make some tricky conditions in Concept 4 suddenly make sense.
Quick check ✅
- What does the word bipotential mean here?
- Which cell makes AMH, and what does AMH do?
Remember this 🌟
Where we're going next → If the female ducts are "free to stay," what exactly do they build? That's Concept 3.