Barbara McClintock was a cytogeneticist best known for her discovery of transposons (a term derived from “transposition”) in maize genes. In 1983, she was the first woman to be awarded an unshared Nobel Prize in Physiology or Medicine. Her work in the field of genetics continues to be of great significance in the study of genetics, cytology, and molecular biology. Her life was a case study of persistence in the face of little recognition from her peers or the public over many years, as well as gender discrimination, and provides an important lesson for science communicators to the effect that the most important discoveries are not always the most quickly recognized—nor the most visible—even in relatively recent times.
Barbara McClintock was born in Hartford, Connecticut, to parents Thomas McClintock, a doctor, and Sara McClintock, a pianist, poet, and painter. Her parents allowed her to follow her own interests rather than imposing a strict regime on her, even allowing her time off from school if she felt like doing something else. This would form much of her adult character, as she followed pursuits she loved solely for the joy of it.
McClintock wanted to go to college, but despite her rather liberal upbringing for a girl at the time, her mother was against it at first. Sara had already persuaded Barbara's older sisters, Marjorie and Mignon, not to go to college, despite Marjorie being offered scholarship money to attend Vassar. Eventually, after Barbara had worked for 6 months while also educating herself in the evenings, her mother relented and allowed her to go to Cornell University.
McClintock flourished at Cornell, and she continued her graduate studies there, gaining her doctorate in botany and genetics in 1927. In the years that followed, up until she left Cornell in 1932, she was a research assistant and botany instructor.
However, she was not simply granted her place in graduate school without any problems. She was originally told she could not enroll to study genetics because she was a woman. But women were allowed to study in the botany department, so she enrolled in cytology (the study of cells) and added in courses from the plant breeding department to combine both areas of interest. In 1931, McClintock and fellow student Harriet Creighton published a paper together called “A Correlation of Cytological and Genetical Crossing-over in Zea Mays.” This paper can be found in The Dynamic Genome (1992), edited by Nina Fedoroff and David Botstein.
By using a new staining technique developed by John Belling, McClintock was able to characterize the maize chromosomes by their lengths, patterns, and shapes. She continued her experiments and publications, consolidating the links she had discovered between cytology and genetics. By her mid-40s, however, McClintock's ideas were seen as so new or radical by some scientists that they were largely ignored, and her dense and complicated writing style did not make her papers easy to follow.
In 1939, she was elected vice president of the Genetics Society of America; she became a member of the National Academy of Sciences in 1944; and in 1945 she served as president of the Genetics Society.
McClintock moved to Cold Spring Harbor, New York, in 1941 to plant her corn there and continue her experiments, funded by a position in the Department of Genetics of the Carnegie Institution of Washington. Her research was largely unaffected by wartime projects, and her work continued as usual. In fact, other wartime problems, such as gas shortages and food rationing, were said to have left little to do at Cold Spring Harbor during that period other than work.
The results from her crop at Cold Spring Harbor lead to her discovery of the concept of transposition. Previously, it was thought that chromosomal elements were fixed in place, like beads on a string, but McClintock realized that they could in fact move into new positions. Noticing some strange patterns and blotches of color in the kernels and leaves of her plants that others had not considered, she discovered a system of control and regulation among genes. She repeated her experiments over 6 years to be sure of her results and then wrote a short paper about transposable genetic elements, published in Proceedings of the National Academy of Sciences and titled “The Origin of Behaviour of Mutable Loci in Maize.” She attempted to present the paper at the Cold Spring Harbor Symposium in the summer but was met with silence and misunderstanding. She tried to explain again in 1956, but by this time her work was even more, not less, difficult for others to follow.
In 1960, researchers Jacques Monod and Francois Jacob created a model of a molecular mechanism for gene regulation. They proposed that protein synthesis is regulated by an operator gene and a regulator gene, not by the structural gene itself as had been previously thought. McClintock was pleased by the similarities between this new work and her own—because now, surely, the scientific world would be able to understand McClintock's work with maize. But despite publishing another paper on the subject, she still could not make people fully appreciate or understand transposition.
The Cold Spring Harbor seminar in 1960 was McClintock's last attempt to be heard by her colleagues. She felt isolated, and younger molecular biologists were becoming more successful with their ideas. Nonetheless, she continued with her work, feeling sure she was right. She won the Kimber Genetics award in 1967 and the National Medal of Science in 1970.
By 1976, transposable elements in bacteria (known as transposons or “jumping genes”) were well documented, but no conclusions had yet been drawn that paralleled McClintock's work on transposable elements in maize. Then, at the 1976 Cold Spring Harbor meeting on DNA insertion elements, plasmids, and episomes, other researchers finally made reference to the parallels between bacteria and maize. Scientists in the later 1970s and early 1980s finally recognized how important “jumping genes” were.
In 1981, then in her 70s, McClintock won eight awards, including some with monetary prizes. Then, on October 10, 1983, she discovered she had won the Nobel Prize in Physiology or Medicine for the discoveries she had made three decades earlier.
Despite her age, she continued to work on her maize research until her death on September 2, 1992, at the age of 90. McClintock's work continues to be relevant to studies going on today, and scientists are still learning from her discovery of transposons. She is also considered a source of inspiration to female scientists for her achievements in the face of sexism.
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