Barbara McClintock: Discoverer of “Jumping Genes”

The woman who would go on to achieve what the Nobel Committee went on to label as “one of the two great discoveries of our time in genetics” almost didn’t go to college – her mother believed that a university education would hurt her prospects of marriage.

Barbara McClintock in her laboratory, 1947. Photo by the Smithsonian via Wikimedia Commons.

Barbara McClintock never did marry, but she did discover genetic transposition – also known as “jumping genes” – in doing so revolutionizing our scientific understanding of genes and chromosomes.  

The Road to Transposons

Having developed a love of science in high school, McClintock persuaded her family to send her to Cornell University. There, she was prevented, as a woman, from majoring in genetics. Instead she dove into the science of cytogenetics, or the study of chromosomes, while also pursuing a degree in botany.

In the early 1920s, women were entering higher education at a higher rate than ever before, but rarely did they achieve the level of full professorship. During this time, fewer than 5% of female scientists in America were able to land jobs at co-ed institutions. McClintock herself was denied a full professorship at graduation – despite an endorsement from the head of her department. She then went on to the University of Missouri as an assistant professor, where after four years she found herself, again and again, blocked from achieving tenure as a woman.

In frustration, McClintock left the University of Missouri to take up a risky one-year fellowship at the Cold Springs Laboratory in New York, which had achieved a reputation as a leading place for genetics research. What began as a one-year fellowship soon bloomed into a lifelong relationship with the institution, where McClintock dove into the study of cytogenetics, specifically in corn.

It was at Cold Spring Laboratory that McClintock discovered what would go on to be her most notable legacy. By cross-breeding certain varieties of corn – for example, corn with purple and waxy kernels with non-waxy, yellow corn – McClintock realized that some varieties of corn had one trait without the other (for example, purple, non-waxy kernels). This was some of the first evidence of what we know today as transposable elements, or transposons – also known as “jumping genes,” which can move positions within or between chromosomes from generation to generation.

Years Unnoticed

At the time, the place of genes on chromosomes was believed to be as fixed as a chair bolted to the floor, but McClintock’s research showed that genes could, and often did, move, in the process becoming either less or more active with the potential for mutations. However, when she presented her theories in 1951, they were met with silence. Not only did her jumping genes fly in the face of then-scientific consensus, McClintock’s object of study – maize – was undervalued by many scientists. McClintock had made one of the largest discoveries in genetics, but for years it went unnoticed.

Yet McClintock never stopped working even as she waited for the scientific community to catch up with her discovery. Starting in 1957, McClintock traveled back and forth to South America under a grant from the National Science Foundation and the Rockefeller Foundation to study different varies of maize, noting the evolutionary characteristics of different varieties and mentoring several graduate students and young scientists in cytogenetics.

It wasn’t until the 1960s that McClintock’s findings were independently verified in bacteria by the scientific community, over a decade after she first discovered genetic transposition in corn. In 1971, McClintock was awarded the National Medal of Science by President Richard Nixon, and in 1981 she became the first recipient of the MacArthur or “genius” grant. Finally, Iin 1983 – over 30 years after first presenting her findings – McClintock was awarded the Nobel Prize in Physiology or Medicine, becoming the first woman to receive an unshared the prize in that category.  

“When You Know You’re Right”

McClintock continued to work at the Cold Springs Harbor Laboratory as a scientist emerita well past her retirement in 1967, when she was awarded the Distinguished Service Award for over 26 years of research by the Carnegie Institution. She died in 1992 at the age of 90, having continued to pursue her research up until the final year of her life.

When asked if she was ever upset about how long it took for her to be recognized, McClintock responded that the act of discovery was rewarding enough in itself: “When you know you’re right you don’t care. It’s such a pleasure to carry out an experiment when you think of something…I’ve had such a good time, I can’t imagine having a better one.”

Further Reading

Barbara McClintock, Biographical Overview – U.S. National Library of Medicine 

Barbara McClintock – The Nobel Prize

Barbara McClintock, Nobel prize-winning plant geneticist – New Scientist

Barbara McClintock – National Science Foundation