What is Nettie Stevens?
{{Infobox scientist |name = Nettie Stevens |caption = |image = Nettie Maria Stevens.jpg |birth_name = Nettie Maria Stevens |birth_date = {{birth date|1861|07|07}} |birth_place = [[Cavendish, Vermont]], United States |death_place = [[Baltimore, Maryland]], United States |death_date = {{death date and age|1912|05|04|1861|07|07}} |death_cause = [[Breast cancer]] |residence = |citizenship = |nationality = |field = [[Genetics]] |work_institutions = [[Bryn Mawr College]], [[Carnegie Institution of Washington]] |education = [[Westford Academy]] |alma_mater = [[Westfield State University|Westfield Normal School]]<br>[[Stanford University]]<br>[[Bryn Mawr College]] |doctoral_advisor = [[Thomas Hunt Morgan]] |known_for = [[XY sex-determination system]] | thesis_title = Further studies on the ciliate Infusoria, Licnophora and Boveria | thesis_year = 1903 | thesis_url = https://www.proquest.com/docview/301753909/791D56E098804FE1PQ/ |author_abbrev_bot = |author_abbrev_zoo = |influences = [[Edmund Beecher Wilson]]<br>[[Thomas Hunt Morgan]] |influenced = |doctoral_students = [[Alice Middleton Boring]] |prizes = |signature = }} '''Nettie Maria Stevens''' (July 7, 1861 – May 4, 1912)<ref>{{Cite web|url=https://www.britannica.com/biography/Nettie-Stevens|title=Nettie Stevens {{!}} American biologist and geneticist|website=Encyclopedia Britannica|language=en|access-date=2019-08-12}}</ref> was an early [[United States|American]] [[geneticist]]. She discovered [[sex chromosome]]s. Stevens saw two kinds of [[sperm]]s in male [[mealworm]]s. One had a large chromosome and one had a small chromosome. They were sex chromosomes, which later became known as the X and Y chromosomes.<ref>{{Cite journal|last=Brush|first=Stephen G.|date=1978|title=Nettie M. Stevens and the discovery of sex determination by chromosomes |journal=Isis|volume=69|issue=2|pages=162–172|doi=10.1086/352001