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Top Comments: Cytogeneticist Barbara McClintock [1]
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Date: 2025-03-30
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This month, I accidentally created a series on great women scientists celebrating Women’s History Month, and tonight, I provide the last installment. Previous diaries were on Emmy Noether, Chien-Shiung Wu, and Maria Goeppert Mayer. Tonight’s subject is another Nobel Prize winner, this time Barbara McClintock.
McClintock was born in 1902 in Hartford, Connecticut. Her parents named her Eleanor, but as she grew and her personality emerged, they decided the name they had given her was too “delicate” and “feminine” for her, so they renamed her Barbara. From a very young age, she was independent and spent much of her time occupied in solitary activity. Throughout her life, this never changed, and she referred to it as her “capacity to be alone.”
She graduated from high school in Brooklyn, NY, in 1919, and then went to Cornell University to further her studies, over the objections of her mother who worried about her “marriageability.” (She never married.) She found her calling after taking a course in genetics, but because Cornell would not allow a woman to major in genetics, she was formally a botany major. She earned her Ph. D. at Cornell in 1927. During her entire career, she used maize (what Americans call “corn”) as the vehicle for her research. In 1931, she and her graduate student Harriet Creighton published a landmark paper demonstrating genetic crossing-over in maize chromosomes. I learned about this process when my sister and I submitted our DNA to 23 and Me, which allows you to compare chromosome content with your DNA matches. I had always assumed that each chromosome gets transmitted from parent to child without alteration, but when comparing my chromosomes with my sister’s, I saw that only pieces of each chromosome matched. Before recombination to form a zygote, sections of each member of a chromosome pair get traded, resulting in a unique combination. While geneticists had previously hypothesized that this process must be taking place, McClintock’s paper proved that it did.
After years of struggling to find a permanent academic position, in 1941, she obtained a position as a research scientist at the Cold Spring Harbor Laboratory in New York, administered by the Carnegie Institution of Washington.
Her greatest discovery was that portions of chromosomal DNA can move from one place to another in the organism’s genome. She called such genes transposable elements (TEs), though they are also called “jumping genes.” She discovered TEs through observing the variety of colors of the kernels in the maize she was studying. She further observed that the color variations were caused by the movement of certain genes within the maize genome, altering gene expression. She performed much of this research in the late 1940s, publishing her first paper on the subject in 1950. To the rest of the scientific community, the thought that chromosomes had the power to modify themselves was alien to the point of heresy. Chromosomes were seen as a library of genetic characteristics, and the books in libraries don’t reorganize themselves on their own, after all. Because she faced such “puzzlement, even hostility” (her words) to her discoveries, she eventually stopped publishing on the topic, though she continued her research.
In time, however, other geneticists began reproducing her work, and determining the importance of these TEs in gene regulation. More than 65 % of the human genome consists of TEs. Studying TEs has been instrumental in understanding much of molecular biology and medicine, from the origin of certain cancers, to a basis for the operation of epigenetics, to the drivers of evolution. McClintock received the 1983 Nobel Prize in Physiology or Medicine unshared. On that, she is quoted as saying
I can't imagine having a better life. It might seem unfair to reward a person for having so much pleasure over the years, asking the maize plant to solve specific problems and then watching its responses.
She died in 1992 at the age of 90.
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