Nobel Prize in Physiology or Medicine 1983
Throughout her career, Barbara McClintock studied the cytogenetics of maize, making discoveries so far beyond the understanding of the time that other scientists essentially ignored her work for more than a decade. But she persisted, trusting herself and the evidence under her microscope.
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1 (of 2) A few labelled samples of Barbara McClintock's maize, with microscope.
Photo: Smithsonian Institution. National Museum of American History
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2 (of 2) Corn stalk specimen.
Photo: Courtesy of the Barbara McClintock Papers, American Philosophical Society
Barbara McClintock almost didn’t go to college. She was a talented student, but her mother believed a college degree would harm her chances of marriage and vetoed her plan to go to Cornell.
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1 (of 2) The McClintock children, ca. 1907. Barbara McClintock is second from the right.
Photo: National Institutes of Health. Courtesy of the Barbara McClintock Papers, American Philosophical Society. Photographer unknown
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2 (of 2) A McClintock family photograph, ca. 1914. Barbara McClintock is third from the right, leaning on the piano.
Photo: National Institutes of Health. Courtesy of the Barbara McClintock Papers, American Philosophical Society.
Fortunately, McClintock’s father returned from the Army Medical Corps in France in time to intervene. In 1919, at the age of 17, McClintock enrolled in the Cornell College of Agriculture. She thrived at college: she joined the student government, played banjo in a jazz band, and excelled in the classroom. It was there that she took the course that would change the course of her life: genetics.
Genetics as a discipline was still new in the 1920s; Cornell offered only one undergraduate course. But McClintock took to it immediately, conceiving a lifelong interest in the field of cytogenetics – the study of chromosomes and their genetic expression.
“No two plants are exactly alike. They’re all different, and as a consequence, you have to know that difference. I start with the seedling and I don’t want to leave it. I don’t feel I really know the story if I don’t watch the plant all the way along. So I know every plant in the field. I know them intimately. And I find it a great pleasure to know them.”
Barbara McClintock
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1 (of 3) A letter from Lewis Stadler (pictured) to Milislav Demerec. A close friend and supporter from Cornell days, Stadler had helped McClintock procure a position at the University of Missouri. Six years later, Demerec brought her to Cold Spring Harbor Laboratory on leave from the university. Stadler writes that although he wants McClintock to return to Missouri, "I hope she will stay at Cold Spring Harbor if she is convinced that would be better for her work."
Courtesy of Cold Spring Harbor Laboratory
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2 (of 3) Page two from a letter from Lewis Stadler (pictured) to Milislav Demerec. A close friend and supporter from Cornell days, Stadler had helped McClintock procure a position at the University of Missouri. Six years later, Demerec brought her to Cold Spring Harbor Laboratory on leave from the university. Stadler writes that although he wants McClintock to return to Missouri, "I hope she will stay at Cold Spring Harbor if she is convinced that would be better for her work."
Courtesy of Cold Spring Harbor Laboratory
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3 (of 3) Barbara McClintock's colleague and supporter Lewis Stadler, with geneticist Esther M. Lederberg at the University of Missouri in the 1950s
Courtesy of Joshua Lederberg
She earned her bachelor’s, master’s and doctoral degrees at Cornell and had great success in her research on the cytogenetics of maize. Even so, it wasn’t easy to find a permanent position in the midst of the Depression. Finally, McClintock was hired as an assistant professor at the University of Missouri in 1936.
McClintock loved working in the lab. “I was just so interested in what I was doing I could hardly wait to get up in the morning and get at it,” she once said.
But for her, teaching was a distraction. She left her university job in 1941 for Cold Spring Harbor Laboratory, a research facility funded by the Carnegie Institution. Freed to focus exclusively on her experiments, McClintock stayed at Cold Spring Harbor until her retirement in 1967 – and even beyond, as a scientist emerita, until her death at the age of 90.
Early in her research at Cold Spring Harbor, McClintock began to study the mosaic colour patterns of maize at the genetic level. She had noted that the kernel patterns were too unstable, and changed too frequently over the course of several generations, to be considered mutations. What was responsible for this? The answer contradicted prevailing genetic theory.
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1 (of 2) Labelled maize. Barbara McClintock discovered that genes could "jump" by studying generational mutations in maize.
Photo: Courtesy of Cold Spring Harbor Laboratory. Photo: Jan Eve Olsson
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2 (of 2) An illustration of corn kernel specimens, included in Barbara McClintock's article in the 'Cold Spring Harbor Symposia on Quantitative Biology' in 1951.
Photo: Courtesy of the Barbara McClintock Papers, American Philosophical Society
As McClintock observed by studying successive generations of maize plants, instead of being locked into place giving fixed instructions from generation to generation, some genes could move around or “transpose” within chromosomes, switching physical traits on or off according to certain “controlling elements.”
Aware that her work departed from the common wisdom, McClintock put off publishing her theories on genetic transposition and controlling elements until other researchers had confirmed her results. At last, in the summer of 1951, she gave a lecture on her findings at the annual symposium at Cold Spring Harbor Laboratory. It didn’t go well. As she later recalled it, the audience was either perplexed by or hostile to her theories. “They thought I was crazy, absolutely mad.”
“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.”
Barbara McClintock
In the face of such resistance to her theories, McClintock stopped publishing and lecturing – she stopped trying to convince others – but she never stopped pursuing her theories. “I just knew I was right,” she said later. “Anybody who had had that evidence thrown at them with such abandon couldn’t help but come to the conclusions I did about it.”
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1 (of 2) McClintock's diagram of the BreakageFusionBridge cycle.
Courtesy of the Barbara McClintock Papers, American Philosophical Society
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2 (of 2) Corn specimens photographed in 1966, when Barbara McClintock was studying the evolution of maize in South America.
Photo: Courtesy of the Barbara McClintock Papers, American Philosophical Society
Finally, in the mid-1960s, the scientific community began to come to the same conclusions, validating her findings and giving her the credit that was long overdue. McClintock received the Nobel Prize more than 30 years after making the discoveries for which she was honoured.
“Over the many years, I truly enjoyed not being required to defend my interpretations. I could just work with the greatest of pleasure. I never felt the need nor the desire to defend my views. If I turned out to be wrong, I just forgot that I ever held such a view. It didn't matter.”
Barbara McClintock
Barbara McClintock made discovery after discovery over the course of her long career in cytogenetics. But she is best remembered for discovering genetic transposition (“jumping genes”). Understanding the phenomenon is still fundamental to understanding genetics, as well as related concepts in medicine, evolutionary biology, and more.
Beyond her discoveries, though, McClintock’s legacy is one of uncommon persistence. As she put it, “If you know you are on the right track, if you have this inner knowledge, then nobody can turn you off… no matter what they say.”