Nettie Stevens was a cytogeneticist. She received her PhD from Bryn Mawr in 1903 and then studied in Europe. She is the discoverer of the chromosomal determination of sex (those X and Y chromosomes that determine whether the baby is a boy or girl) and published about thirty-eight professional papers.

Nettie Stevens was a cytogeneticist. She received her PhD from Bryn Mawr in 1903 and then studied in Europe. She is the discoverer of the chromosomal determination of sex (those X and Y chromosomes that determine whether the baby is a boy or girl) and published about thirty-eight professional papers.