Through her research with mealworms, Nettie Stevens identified that males produced reproductive cells with two types of chromosomes, while female reproductive cells only had one type of chromosome. This led her to deduce the genetic-based sex determination.

While the chromosomal sex determination is commonly attributed to Nettie Stevens, it has also been credited to Edmund Wilson, who encounter similar findings at a similar time. However, both Stevens and Wilson were sometimes forgotten in biology textbooks, where the discovery is often erroneously credited to Thomas Hunt Morgan.