By TIME Staff
July 7, 2016

That X and Y chromosomes combine to determine gender, now common knowledge taught in biology classes the world over, was discovered by pioneering American scientist Nettie Stevens. On what would have been her 155th birthday, Google is celebrating her immense contribution to the field of genetics with a Doodle.

Stevens was born in Cavendish, Vt. in 1861, and grew up in an era where job opportunities for women were severely restricted. After studying at Stanford University, she got her PhD at Bryn Mawr College, where she did the bulk of the research that led to her breakthrough.

Stevens died of breast cancer in 1912, but, as Google said, “her discovery lives on.”

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