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Nettie Stevens (July 7,1861- May 4, 1912) was a renowned American geneticist whom discovered that people have determined sex chromosomes .In 1905, after reading Gregor Mendel's new paper on genetics called, Verhandlungen des naturforschenden Vereines in Brünn. After reading this article she studied male beetles. In the process of studying the beetles she found that the male produced 2 types of sperm. One of the types had a small chromosome, while the other had a large chromosome. She then studied how each fertilized eggs. She found the large fertilized the egg and all of the offspring turned out to be female, and the small made male offspring. Nettie Stevens discovery became the study of the XY sex-determination system.

Biography
Nettie Maria Stevens was born in Cavendish, VT on July 7, 1861. Her parents were Ephraim Stevens and Julia Adams-Stevens. When Nettie turned only 2 years old, her mother passed away. Not long after her mother's passing, Ephraim married Ellen Thompson. After a few years and a younger sister, Emma Stevens, they decided to relocate to Westford, MA. Nettie Stevens interest in science probably came about in summer classes at Martha's Vineyard in 1890 and 1891. Nettie Graduated Westford Academy high school at the age of 18 in 1880. Nettie's teachers noticed how much potential she had while going through school. After graduating she became a teacher until 1892. This is when she had been accepted into Stanford University to study for a bachelor's degree in Physiology. She accomplished her degree in 1899 at the age of 38 years old. She then went on to get her Master's in 1900. After getting her master's she transferred over to Bryn Mawr College and got her PhD in 1903. Before attaining her PhD, she had already had 9 papers published. Two of the leading American biologists Edmund Beecher Wilson and Thomas Hunt Morgan were a big part of Stevens education and also publishing of her papers. Stevens remained at the college as a research fellow in biology for a year, as reader in experimental morphology for another year, and as associate in experimental morphology from 1905 until her death 1912. She passed from breast cancer May 4, 1912 in Baltimore, MD. She never married or had any children to pass her incredible smarts to.

Advancements made in Science
At the beginning of Nettie's research in sex determination, most scientists had no clue how the sex of a cell was determined. They believed that the nutrition and temperature the cell was getting would determine the sex. Before starting her research in 1904, she saw that there wasn't a huge connection between Gregor Mendel's paper on genetics. She set out to get a grant to be able to do research.

After receiving the grant, she used germ cells of aphids to examine possible differences in chromosome sets between the two sexes. One paper, written in 1905, won Stevens an award of $1,000  for the best scientific paper written by a woman. Her major sex determination work was published by the Carnegie Institution of Washington in the two part monograph, "Studies in Spermatogenesis,"  which highlighted her increasingly promising focus of sex-determination studies and chromosomal inheritance. In 1908, Stevens received the Alice Freeman Palmer Fellowship from the Association of Collegiate Alumnae, now the American Association of University Women. During that fellowship year, Stevens again conducted research at the Naples Zoological Station and the University of Würzburg, in addition to visiting laboratories throughout Europe.

Although Nettie didn't teach at Bryn Mawr College, she still conducted research that lead her to have 38 published papers. Her papers include several major contributions to further the emerging concepts of chromosomal heredity. By experimenting on germ cells, Stevens interpreted her data to conclude that chromosomes have a role in sex determination during development. Stevens found that when looking at the sperm cells of male beetles there are 2 types of chromosomes. She did tests to see what the large and small chromosomes had to do with the sex of the cell. As is turned out the larger decided that the cell was female and the small would make it a male. Stevens continued her research on the chromosome makeup of various insects, discovering supernumerary chromosomes in certain insects and the paired state of chromosomes in flies and mosquitoes.

As a result of her research, Stevens provided critical evidence for Mendelian and chromosomal theories of inheritance. Stevens was quick to see the possibilities that opened up from McClungs hypothesis in comparison to Mendelian theory of inheritance. She was so determined to study how sex chromosomes work.

Quotes about Nettie

 * Modern cytological work involves an intricacy of detail, the significance of which can be appreciated by the specialist alone; but Miss Stevens had a share in a discovery of importance, and her work will be remembered for this, when the minutiae of detailed investigations that she carried out have become incorporated in the general body of the subject. - Thomas Hunt Morgan


 * Miss Stevens’s work is characterized by its precision, and by a caution that seldom ventures far from the immediate observation. Her contributions are models of brevity—a brevity amounting at times almost to meagerness.- Thomas Hunt Morgan
 * Her [Nettie Stevens] single-mindedness and devotion, combined with keen powers of observation; her thoughtfulness and patience, united to a well-balanced judgment, account, in part, for her remarkable accomplishment. -Thomas Hunt Morgan
 * She [Nettie Stevens] was a trained expert in the modern sense—in the sense in which biology has ceased to be a playground for the amateur and a plaything for the mystic. - Thomas Hunt Morgan

Reference section
Nettie Stevens https://scientificwomen.net/women/stevens-nettie-102 https://www.famousscientists.org/nettie-stevens/ https://www.famousscientists.org/nettie-stevens/

External links section
https://www.famousscientists.org/nettie-stevens/ https://scientificwomen.net/women/stevens-nettie-102 http://www.dnaftb.org/9/bio.html https://www.jstor.org/stable/230427?seq=3#metadata_info_tab_contents https://todayinsci.com/S/Stevens_Nettie/StevensNettie-Quotations.htm