Thanks to the research of Nettie Stevens, we know that males are responsible for determining the sex of their children.
To highlight her contributions to our understanding of chromosomes, Google launched a doodle to mark her 155th birthday on Thursday.
Born in 1861, Stevens grew up in a post-Civil War America in which job opportunities for women were limited to being teachers, nurses, or secretaries. But Stevens wanted to be a scientist, so she became a teacher, allowing herself to continue studies when she had enough money to do so.
After earning advanced degrees from Stanford University and Bryn Mawr College, she began working as a research scientist at the age of 39. Despite her late start in the field, Stevens made observations that advanced our understanding of sex determination.
During her studies of the mealworm, Stevens discovered that males produced sperm with both X and Y chromosomes, while females produced eggs with only X chromosomes. From this, she concluded that sex determination is based on the presence or absence of the Y chromosome.
Stevens died of breast cancer on May 4, 1912, at the age of 50. Despite her relatively brief time as a scientist, she is credited with expanding the fields of embryology and cytogenetics, the study of chromosomes.