Nettie Stevens

Nettie Maria Stevens (July 7, 1861 – May 4, 1912) was the American geneticist who discovered sex chromosomes. In 1905, soon after the rediscovery of Mendel's paper on genetics in 1900, she observed that male mealworms produced two kinds of sperm, one with a large chromosome and one with a small chromosome. When the sperm with the large chromosome fertilized eggs, they produced female offspring, and when the sperm with the small chromosome fertilized eggs, they produced male offspring. The pair of sex chromosomes that she studied later became known as the X and Y chromosomes.

Early life Nettie Maria Stevens was born on July 7, 1861, in Cavendish, Vermont, to Julia (née Adams) and Ephraim Stevens. In 1863, after the death of her mother, her father remarried and the family moved to Westford, Massachusetts. Her father worked as a carpenter and earned enough money to provide Nettie and her sister, Emma, with a strong education through high school. won Stevens an award of $1,000 which highlighted her increasingly promising focus of sex-determination studies and chromosomal inheritance. 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.

Career

Stevens was one of the first American women to be recognized for her contribution to science. Most of her research was completed at Bryn Mawr College. The highest rank she attained was Associate in Experimental Morphology (1905–1912). Edmund Wilson worked on spermatogenesis preparations simultaneously with Stevens's studies. He performed cytological examination only on the testes, that is he did not examine the female germ cells (eggs) but only the male germ cells (sperm) in his studies. His paper stated that eggs were too fatty for his staining procedures. After reading the papers describing Stevens's discoveries, Wilson reissued his original paper and in a footnote acknowledged Stevens for the finding of sex chromosomes.

Sex determination Although Stevens and Wilson both worked on chromosomal sex determination, many authors have credited Wilson alone for the discovery. In that article, Morgan said she had "a share in a discovery of importance." He described sex linkage of the white gene in the chapter immediately preceding the one in which he reported Stevens's results without mentioning her name, implying that his own laboratory's sex linkage analysis was the basis for understanding sex determination. In an earlier letter of recommendation, he wrote, "Of the graduate students that I have had during the last twelve years, I have had no one that was as capable and independent in research as Miss Stevens."

Death At 50 years old, and only 9 years after completing her Ph.D., Stevens died of breast cancer on May 4, 1912, in Baltimore, Maryland. Her career span was short, but she published approximately 40 papers. She was buried in the Westford, Massachusetts cemetery alongside the graves of her father, Ephraim, and her sister, Emma.

Quotes

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|following Stevens's death in 1912 (The Scientific Work of Miss N. M. Stevens. Science, Vol. 36 (No. 928), October, 1912)

To celebrate her 155th birthday, on July 7, 2016, Google created a doodle showing Stevens peering through a microscope at XY chromosomes.

On May 5, 2017, Westfield State University honored Stevens through the naming ceremony of the Dr. Nettie Maria Stevens Science and Innovation Center. The center is where the university's STEM-related degree programs in Nursing and Allied Health, Chemical and Physical Sciences, Biology, Environmental Science and the then soon-to-be launched master's degree program in Physician Assistant Studies are all based.