Nettie Stevens discovered XY intercourse chromosomes. She did not get credit because she had two X’s.

Nettie Stevens discovered XY intercourse chromosomes. She did not get credit because she had two X’s.

In the change regarding the century that is 20th biologist Nettie Stevens had been driven to fix a clinical secret which had perplexed mankind for millennia. The secret ended up being so easy but daunting: Why do men be girls and boys become girls? Inside her pioneering work on Bryn Mawr university, Stevens — whoever birthday celebration is today, July 2 — found the intercourse chromosomes that make the huge difference.

Before Stevens, we had been utterly clueless about how embryos become guys or girls

As a result of Stevens’s work — as well as the work that built upon it — we now understand that sex is hereditary, and therefore dads’ sperm in particular determine the intercourse of offspring. More →