Nettie Stevens was an outstanding student, completing her four year degree in half the time and graduating top of her class. After starting out her career as a school teacher, she returned to college and completed her BA and MA degrees. Finally, at the age of 39, she was able to start working as a researcher. Nettie researched sex determination, and by analysing insect chromosomes she discovered that male mealworms made reproductive cells with both X and Y chromosomes, whereas females made cells with just X chromosomes. She realised that sex was inherited through the chromosomes, and that males determine the gender of offspring. This discovery was important it was the first time someone had shown that observable differences in chromosomes could be related to observable differences in physiology. However, at the time it was believed that gender was inherited from the mother or from the environment, and Netties theories were not widely accepted Nettie continued to research and teach, before she passed away from breast cancer in 1912, having had just a very short scientific career, but one with huge developments and contributions.
