Four Women Who Made Major Contributions to Genetics and Medicine (Whose names you might not know)

Share with your network

Nettie Stevens: Discoverer of Sex Chromosomes

Women like Nettie Stevens, who were born in the early 1860s, didn’t have a plethora of career options to choose from. They could either be secretaries, or they could be teachers. Stevens went down the teaching route. What she really wanted to do, however, was continue her education. Eventually, at the age of 36, she saved up enough money from her teaching jobs, moved from Vermont to California, and enrolled in Stanford University, and later in Bryn Mawr college for her PhD.

Stevens entered the field of genetics at a time when the field was rapidly expanding. Mendel’s seminal work on the principles of inheritance had been rediscovered in 1900, and in a few short years, Thomas Morgan – who taught Stevens at Bryn Mawr – would go on to show that genes are carried on chromosomes. While this might seem unremarkable now, Morgan’s research provided physical evidence for the heredity described by Mendel. However, despite the increasing evidence that physical traits are determined by genes, scientists still believed that either the mother’s environment or the chemical balance of the cytoplasm of eggs determined sex.

Nettie Stevens’ research put the issue to rest. Stevens studied mealworms – insects that resemble garden grubs – and after spending endless hours peering through microscopes, found that during spermatogenesis, the 20 chromosomes of the mealworm form “9 symmetrical pairs and 1 unsymmetrical [pair] composed of [a] small chromosome and a much larger mate.” This asymmetrical pair, she observed, was replaced by a tenth symmetrical pair during the formation of egg cells. She also found that somatic (non-reproductive) cells of mealworms followed a similar pattern: 10 symmetrical pairs of chromosomes in females, and 9 symmetrical pairs and 1 asymmetrical pair in males. This discovery was conclusive proof that chromosomes – in the form of the X and Y chromosomes in most animals – were what led to sex determination, and not maternal characteristics.

Nettie Stevens unfortunately died of breast cancer at the age of 50, a mere four years after she discovered sex chromosomes. Her reputation – both then and now – does not match the significance of her research. Morgan, her mentor and professor, is considered the most influential figure in modern genetics and often gets credited for all chromosome-related discoveries. Morgan’s name appears frequently in relation to his research on chromosomes, but Nettie Stevens’ doesn’t.

Alice Ball: The chemist who developed a cure for leprosy

Alice Ball grew up around chemicals. Her grandfather, James Presley Ball, was a famous African American photographer. Chemicals used in developing photographic prints, such as silver, iodine, chlorine, and bromine were likely part of her life years before she entered a chemistry lab.

Ball was born in Seattle on July 24, 1892. Her family moved to Hawaii in 1903 hoping that the salubrious weather would alleviate her grandfather’s arthritis. Her family moved back to Seattle in 1905, following her grandfather’s death. She earned two bachelor’s degrees in Pharmaceutical Chemistry and the Science of Pharmacy in 1912 and 1914, respectively. She then decided to pursue a master’s degree at the College of Hawaii, now called the University of Hawaii, and eventually became the first female and first African-American chemistry professor at the College.

Ball became an expert in extracting active ingredients from plants, and caught the attention of Harry T. Hollmann, medical director of the Kahili Leprosy Hospital. He had been trying to treat leprosy patients but hadn’t been making much progress. In a pre-antibiotic world, there was no clear cure for leprosy, although a potential candidate had been known for years. Chaulmoogra had been used to alleviate skin diseases, including leprosy, in India and China for centuries. Eventually, in the 19th Century, Western doctors started experimenting with Chaulmoogra oil to see if it could be used to treat leprosy. But success had been limited. Ingestion had proven to be ineffective and injecting the oil had proven disastrous – the viscous oil clumped under the skin to form blisters, due to which the patient’s skin looked as though it “had been replaced by bubble wrap.” What doctors needed was a form of Chaulmoogra oil that could be absorbed by the body.

Enter Alice Ball, the 23-year-old chemist whose master’s thesis was on the extraction of the active ingredient from a root called the Ava root. In less than a year, Ball devised a way to create a water-soluble injectable form of Chaulmoogra oil.

Ball died shortly thereafter, on December 31, 1916, at the age of 24. It is unclear why she died, although it is possible that she could have gotten chlorine poisoning while teaching in the lab.

Ball did not live to see 84 patients in the Hospital get cured because of the extraction method she had developed. She was also not given due credit for her discovery, as Arthur Dean, president of the College of Hawaii, published Ball’s extraction technique as his own. In was only in 1922 that she got credit for her work, when Hollmann, the surgeon who had initially encouraged her to develop the drug, wrote about the extraction process and called it “The Ball Method.” The injectable form of Chaulmoogra oil became the principal method of treating leprosy until the 1940s. In 2000, then Hawaii Lieutenant Governor Mazie Horono declared February 29 Alice Ball Day.

Barbara McClintock: Discoverer of Transposons

From the time Barbara McClintock was a young girl, it was clear that she was not going to grow up to become a conventional woman. She preferred sports over dolls, and her mother even made her bloomers so that she would be able to play all the sports she wanted “unhindered by dresses.” As her desire to pursue higher education grew, however, her mother’s support of her idiosyncrasies became less enthusiastic. Worried that an academic daughter would be unmarriageable, she was reluctant to allow McClintock to go to college. Her father interfered, however, and McClintock went off to Cornell to pursue a degree in Agriculture.

By the time she graduated, McClintock became an expert at preparing cells for the microscope. She began studying maize and became so familiar with maize chromosomes that she noticed that certain sections of the chromosome broke off and reattached to different chromosomes and that this corresponded with changes in the coloration of the maize. McClintock called these regions controlling elements (they are now called transposons). This discovery greatly expanded what scientists believed that genes could do. Previously genes were thought to be stationary – like, as the popular analogy goes, beads on a string. McClintock developed a strong reputation in the scientific community and was elected president of the Genetics Society of America in 1945, becoming the first woman to serve in the position.

However, what McClintock really wanted to study was how genetic expression was regulated. It was a question that had plagued scientists for decades: how could neurons and skin cells can look so different despite having the same genetic code? McClintock hypothesized that if a transposon landed near a gene, it would turn off its expression, and turn it on when it left. She presented this theory at a prominent symposium in 1951, but her theory – lacking data to back it up – baffled scientists. McClintock withdrew from the scientific limelight after the symposium and didn’t publish her research after 1953. In 1983, Evelyn Keller published a popular biography of McClintock that brought McClintock back into the public consciousness. McClintock was awarded the Nobel Prize in Physiology or Medicine the same year – the first and only woman to receive an unshared Nobel Prize in the category. However, despite the honor, she never succeeded in proving the regulatory functions of transposons, and indeed, subsequent research showed that it is proteins such as transcription factors, promotors, enhancers, and repressors that control gene expression.

Tu Youyou: A cure for malaria

Tu Youyou was born in 1930 to a family that greatly valued education. At university, she trained under a phytochemist who taught her how to extract active ingredients from plants using appropriate solvents. After graduating, Youyou was recruited to the Institute of Materia Medica, Academy of Traditional Chinese Medicine. Her interest in traditional medicine had deep roots. Growing up, she had seen folk recipes being used to treat a variety of diseases and had seen that some of them were quite effective. The Institute of Chinese Materia Medica provided a unique environment for the combination of Traditional Chinese Medicine and Western medicine. It was an institution where historians, who poured over ancient recipes, and chemists and medical doctors, who had modern tools at their disposal, worked side by side.

It was under these conditions that in 1967, Youyou was tasked with developing a drug to treat chloroquine-resistant malaria. Many Chinese and American soldiers were dying due to malaria in Vietnam – and both the United States and China launched campaigns to develop a treatment, and Youyou was recruited to the Chinese campaign.

Youyou’s team collected over 2000 recipes based on over 600 herbs. One of the most promising candidates was Qinghao, the Chinese name for six herbs falling under the genus Artemisia. Handbooks detailing traditional recipes were helpful in refining their techniques of extraction. One recipe, for example, made Youyou’s team attempt a cold extraction instead of performing extractions at boiling temperatures, leading to better results. Youyou extracted the active ingredient from Artemisia annua and it proved to be effective against rodent malarias. In the absence of robust protocols on how to conduction clinical trials in China in the 1960s and 1970s Youyou and her team volunteered inject themselves to ensure that the active ingredient wasn’t toxic. The team then used the drug to treat 21 malaria patients and saw that their fever disappeared. Their drug was 100 percent effective.

Youyou was awarded the Lasker DeBakey Clinical Medical Research Award in 2011 and the Nobel Prize in Physiology or Medicine in 2014 for her work, which, the presenter of the Lasker award described as “arguably the most important pharmaceutical intervention in the last half-century.”

Check out our blog honoring five of Emory’s female inventors and their work here.


Nettie Stevens

Alice Ball

Barbara McClintock

  • “Barbara McClintock and the discovery of jumping gene” by Sandeep Ravindran:

  • “’The Real Point is Control’: The Reception of Barbara McClintock’s Controlling Elements” by Nathaniel Comfort:

  • The Tangled Field by Nathaniel Comfort

  • The Violinist’s Thumb: And Other Lost Tales of Love, War, and Genus, as Written by Our Genetic Code by Sam Kean1

Tu Youyou