The Google Doodle today features Nettie Stevens for what would've been her 155th birthday. As Vox writes, Stevens uncovered the connection between the Y chromosome and maleness by studying mealworms. "Thanks to Stevens's work — and the work that built upon it — we now know that sex is hereditary, and that dads' sperm in particular determine the sex of offspring," it adds.
Stevens was born in Vermont in 1861, but Vox notes that she was a latecomer to science, enrolling at Stanford University at age 35 where she earned a bachelor's and a master's degree. She then sought a doctorate at Bryn Mawr College where she tackled the genetics of sex determination. By examining chromosomes from mealworms under the microscope, Stevens found that both male and female mealworms had 20 chromosomes, but one of the chromosomes in the male worms was smaller than the others. "This seems to be a clear case of sex determination," Stevens wrote in her Studies in Spermatogenesis report.
But, Vox adds, Stevens rarely gets the credit for linking chromosomes to sex determination; that instead goes to E. B. Wilson, who was working on the same question in a different species. He found that males of that species harbored one fewer chromosomes than females, but he also thought there were environmental influences at play, Vox says. It adds that Wilson likely gets credited for this over Stevens, even though she made the stronger argument, because he was a higher-profile researcher and male.
According to the Independent, Nobel Prize-winner Thomas Morgan, who also studied chromosomes, once wrote that Stevens's "single-mindedness and devotion, combined with keen powers of observation; her thoughtfulness and patience, united to a well-balanced judgment, accounts, in part, for her remarkable accomplishment."
Stevens died in 1912 of breast cancer.