Alright, moving along then.
Wow. I didn't even realize there were geneticists (other than Mendel) back in the ninteenth century. And, on top of that, I didn't realize a woman had such an important role in the discipline.
Along with a geneticist named Edmund Beecher Wilson, she discovered one of the few things that almost everyone knows about genetics. (That's her on the right, by the way.) Using the same fruit fly that I mentioned below, she found the chromosomal basis for sex determination: the X and Y chromosomes.
So you know how this goes. Females have two X chromosomes, males have an X and a Y. And that genetic difference drives all the physical differences that appear between males and females in most species (there are some very notable exceptions).
She travelled in some pretty awesome company: Thomas Hunt Morgan was one of her professors (he later won a Nobel Prize for his work establishing that same fruit fly as a model system for studying genetics and embryology).
Nettie herself was born to working-class parents in Vermont. She taught for 10 years before saving enough money to go to university, which she attended at Stanford, graduating with a master's degree. She worked then at Bryn Mawr College in Philadelphia, but died of breast cancer before she was able to receive the research faculty position she desired.
Her position in history is somewhat controversial. Usually Edmund Beecher Wilson seems to be given the credit for the X and Y chromosome discovery. Her obiturary, published in Science and written by Morgan, seems to indicate that he considered more a technician than a scientist. Wikipedia also claims that she brought the fruit fly to Morgan's lab in the first place (although my copy of Fly: The Unsung Hero of Twentieth Century Science doesn't mention her at all).
Wikipedia (of course!)
DNA From The Beginning