Thought I'd start a thread to discuss real life examples of where biology is the relevant factor in discrimination against women.
Here's mine.
A few years ago, I and a group of other women had to threaten to take our then employer to court to get equal pay. (Yup, nearly 50 years after the equal pay act this still happens). They settled after conciliation through ACAS.
Was our employer a sexist dinosaur? Picking on us for our fluffy lady brains?
No, it was actually a case of cock-up rather than conspiracy, but very illustrative of the way structural sexism works.
They had very long pay scales with very small increments, leading to typically seven to ten years before any employee reached "rate for the job". They also had a performance related pay system which meant you got a small increment if you got an average performance rating, and a very slightly larger increment if you got a better-than-average performance rating. They also had a system (meant to help not to discriminate against women) where women on maternity leave got awarded a default "average" performance rating for the year.
Don't get me wrong - it was a crap pay system for everyone - but particularly, and demonstrably crap for women.
Because the net result of this was that seven, ten years into a job role, you could (and often did) find yourself sitting next to a male colleague who was doing precisely the same job as you, no more nor less competently, who earned more than you.
This was a situation where a firm, with the best of intentions (they'd even thought about how to handle maternity leave) still managed to create a system which was institutionally sexist, because women get pregnant and men don't. (Not all women; but no men).
Sex, not gender expectations, was the driving factor behind this cock-up.