Monday, July 8, 2013
Stevens research while at Bryn Mawr was studying the chromosomes of sex cells of meal worms. Sex cells are the cells produced by males and females that give rise to progeny. These cells have half the number of chromosomes that normal cells do. When male and female sex cells combine, a process called fertilization, it gives rise to a single cell with half of its chromosomes from the father and half from the mother that will eventually develop into progeny. Stevens noted in her research that some male sex cells have a chromosome not found in female sex cells. She proposed that this extra chromosome was responsible for determining the sex of the offspring. Today we call this extra chromosome the Y-chromosome and when a male sex cell, with a Y-chromosome, fertilizes an egg the offspring will be male. Half of male sex cells have an X-chromosome and when it fertilizes a female sex cell the offspring will be female. At the time it was believed that the gender of offspring was determined by the mother and environmental factors and Stevens' research was not widely accepted. Today we know that the sex cells of the father, with either Y or X chromosomes, determine the gender of the offspring through the mechanism discovered by Stevens.
Stevens died of breast cancer on May 4, 1912 at the early age of 39.
DNA Learning Center; "Nettie Maria Stevens (1861-1912)"; Retrieved from: dnaftb.org
Scitable; "Nettie Stevens: A Discoverer of Sex Chromosomes"; Retrieved from: nature.com
Nettie Stevens Wikipedia Entry