Nettie Stevens (1861 - 1912)
Dr. Nettie Stevens was a geneticist and one of the first scientists to discover that sex is determined by a specific set of chromosomes. Her early studies in sex determination began with insect models. Dr. Stevens discovered that in some insect species, chromosomes are different among the sexes. From this research, she developed evidence for the chromosomal theory of inheritance, theorizing that males determine the sex of offspring and chromosomes play a role in sex determination.