Nettie Maria Stephens (1861-1912) was a biologist and geneticist.
In 1905 she discovered the X and Y sex chromosomes while working with beetles.
Stevens was able to provide proof for Calvin Bridges' hypothesis that genes were contained in chromosomes. She did this by examining the chromosomes of the fruit fly Drosophila melanogaster. Bridges wrote a couple of papers presenting the proof. He thanked her as "Miss Stevens" without stating what her contribution was nor referring to her PhD.