Studies in Spermatogenesis (Vol.1&2)

Studies in Spermatogenesis is a two part monograph written by American geneticist Nettie Maria Stevens which highlighted her increasingly promising focus of sex-determination studies and chromosomal inheritance. 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.

Nettie Maria Stevens (1861-1912) was an American geneticist credited with the discovery of sex chromosomes. Stevens was one of the first American women to be recognized for her contribution to science. Her record of 38 publications includes several major contributions that 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.