Image of Barbara McClintock (left) via the Library of Congress. Image of “Nettie Stevens with microscope, 1909" (right) via Bryn Mawr College Photo Archives, BMC-Photo Archives, Series I, PA_Stevens_Nettie_005, Bryn Mawr College Special Collections. — *Image of Barbara McClintock (left) via the* *Library of Congress. Image of “Nettie Stevens with microscope, 1909" (right) via* *Bryn Mawr College Photo Archives, BMC-Photo Archives, Series I, PA_Stevens_Nettie_005, Bryn Mawr College Special Collections.*

Three women who made groundbreaking discoveries that revolutionized both the study of genetics and the practice of medicine

The study of genetics has led to incredible leaps in understanding of health, heredity, and medicine. The more we learn about genes and their expression, the more we're able to predict risk factors, understand more about health conditions, and develop new treatments for disease.

Research scientists play an important role in medicine and women have been active researchers in genetics throughout the history of the field. As is often the case, many of their contributions did not receive the same attention and acclaim as those of their male colleagues. Still, women were there, doing research, making discoveries, and adding to a body of knowledge that continues to influence medicine to this day.

Here are just three of the women who made groundbreaking discoveries that revolutionized both the study of genetics and the practice of medicine.

Barbara McClintock

Barbara McClintock was a genetics researcher who studied maize (corn) cytogenetics. She is best known for discovering “jumping genes.”

Born in 1902, McClintock studied botany at Cornell, obtaining undergraduate, masters and doctoral degrees from the university. She pursued post-doctoral training in the US and abroad and was an assistant professor at the University of Missouri at Columbia from 1936 to 1940.

In 1941, she accepted a one-year research position at the Carnegie Institution of Washington's Department of Genetics at Cold Spring Harbor. She would remain at the institution until 1967 and remain affiliated with it until her death in 1992.

In the late 1940s, McClintock discovered that some genes were not always locked into place. Known as “transposable elements,” “transposons,” or “jumping genes,” these genetic elements can move to a different position within a chromosome according to certain “controlling elements.” This can switch physical traits on or off. McClintock's research was contrary to the prevailing view at the time that genetic material was stable and consistent as it was passed from generation to generation.

When McClintock published her findings in the 1950s, she did not immediately revolutionize genetics. She later said, “It didn’t bother me, I just knew I was right. Anybody who had had that evidence thrown at them with such abandon couldn’t help but come to the conclusions I did about it.”

Her day of vindication came later when molecular biologists found transposition in bacteria, viruses, and yeast. Transposition has had applications in antibiotic-resistant bacteria, viral infections, cancer, immunology, and genetic engineering.

In 1981, McClintock was the first recipient of the MacArthur Foundation Grant. In 1983, at the age of 81, she received the Nobel Prize in Physiology or Medicine. She was the first woman in that category to receive the prize alone, without sharing it with a male scientist.

Nettie Maria Stevens

How is the sex of offspring determined? For most of history, it was a mystery. Then, in the early years of the 20th century, Nettie Stevens discovered the role of XY sex chromosomes in determining sex.

Born in 1861 in Vermont, Stevens was an excellent student, one of few women in her high school's graduating class. Following her graduation, she became a teacher to earn money for college. Her true enthusiasm was for biology.

She paid for her education piecemeal as a teacher until she could afford it, eventually graduating from Westfield State University. She then pursued a master’s degree at Stanford University, followed by a doctorate obtained in 1903 from the prestigious women’s institution, Bryn Mawr College. During her graduate studies, she developed precise microscopic skills and interests in histology, physiology, and cell division and regeneration. She was finally able to begin her career as a research scientist at the age of 39.

While studying insects, Stevens found that males of the species had XY chromosomes and the females XX. From this, she deduced that sex is a chromosomal characteristic, inherited from the father. This countered prevailing beliefs at the time that sex was determined from maternal or environmental factors. Other scientists, more prominent and male, came to similar conclusions around the same time, and Steven’s contributions have often been overshadowed historically. Her research career was cut short by her death of breast cancer in 1912.

Rosalind Franklin

Rosalind Franklin was a British scientist who played a crucial role in understanding the structure of DNA.

By the time she was in high school, Franklin knew she wanted to be a scientist. She trained as a physical chemist, pursuing both her undergraduate and doctoral studies at Cambridge. While an undergraduate, she wrote, “Science and everyday life cannot and should not be separated. Science, for me, gives a partial explanation of life.”

Following her doctoral studies, she spent three years in Paris at the Laboratoire Central des Services Chimiques de L'Etat, where she learned x-ray diffraction. Then she returned to England for a research position at King's College, where she ran a DNA project.

Franklin created x-ray diffraction photographs that showed the double-helix structure of DNA molecules. Her resulting data from analyzing these photographs, and the photographs themselves, were critical to DNA research published by Watson and Crick, but her contributions were, at best, underplayed and overshadowed. She moved on to Birkbeck College, where she did pioneering work on viruses, until her death of ovarian cancer at the age of 37.

Her contributions to the discovery of DNA structure became better understood in the decades following her death, as biographies and documentaries highlighting her life and career gained public attention.

Leading the Way

These days, women working in genetics don’t have to wait decades to be recognized for their contributions to science. In 2020, two women, Emmanuelle Charpentier and Jennifer A. Doudna, shared the Nobel Prize in Chemistry for their work on DNA editing, the only science Nobel to be won by two women. The legacy of McClintock, Stevens, and Franklin lives on through the brilliant women working in genetics today.