Barbara McClintock, Geneticist & Nobel Prize Winner in Physiology or Medicine

Barbara McClintock was born on June 16, 1902 in Hartford, Connecticut to Thomas Henry McClintock and Sara Handy McClintock. The McClintock family, with Barbara’s three siblings, moved to Brooklyn, New York when Barbara was six years old. She graduated from Erasmus Hall High School in Brooklyn and went on to attend Cornell University and receive her Bachelors, Masters, and Ph.D. in botany, all in 8 years. While women were not allowed to study genetics at Cornell, she joined a small group that studied maize (corn) cytogenetics, that is, the genetic study of maize at the cellular level. Barbara remained at Cornell as an instructor until 1931 and worked with graduate student Harriet Creighton on experiments that proved that the genetic phenomenon “crossing-over” could be explained by examining cells. In several organisms, one chromosome of every pair is inherited from one parent. It had long been speculated that during cellular division (meiosis), parts of one chromosome inherited from one parent are able to change place with their analogous parts on the chromosome from the other parent. The two researchers were able to verify their results by cross-checking a genetic trait with a part of a chromosome seen under a microscope. Their collaborative paper, known as Proceedings of the National Academy of Sciences, has been vital in modern understanding of genetics. In her acceptance speech for her Nobel Prize, she said that it was her experiences at Cornell that were the “most influential in directing [her] scientific life.”

Additionally, in 1931 with a fellowship from the National Research Council, Barbara began working at the University of Missouri. Her research focused on the effect of X-rays on corn chromosomes, which paved the way for her discovery of translocations, inversions, deletions and ring chromosomes in corn. In 1933, she received a prestigious Guggenheim fellowship to study with renowned German scientist Curt Stern in Berlin. However, at the time, Hitler and the Nazi party were gaining power in Germany and thus, Stern had to flee the country and find work at another institution. McClintock still went to Berlin and met the influential German geneticist Richard B. Goldschmidt, the head of the Kaiser Wilhelm Institute in Berlin. Reflecting on her experience in 1934, she wrote, “I couldn’t have picked a worse time. The general morale of the scientific worker was anything but encouraging. The political situation and its devastating results were too prominent.”

After her time in Berlin, she returned to Cornell and with the Rockefeller Foundation’s aid was able to maintain her position there for 3 years. She was then offered a position as an assistant professor at the University of Missouri and remained there until 1941, when she realised that her “independent” and “maverick” ways were not in line with the University’s image of how a woman scientist was supposed to be. Despite her frustration with her position, her research into maize cytogenetics made great strides and she described the “breakage-fusion-bridge” cycle in which X-ray exposure broke certain chromosomes and then the chromosomes ended up fusing together at their broken ends. Moreover, the breakages continued as the plants grew as fused chromosomes tugged apart during cell division.

In 1941, Barbara was offered a full-time research position at the Carnegie Institution of Washington’s Department of Genetics at Cold Spring Harbor, where she would carry out research that would one day win her a Nobel Prize in Medicine: the discovery of transposition. Transposition is the principle that genetic elements on a chromosome can sometimes change position, and this causes nearby genes to become active or inactive. While this research was certainly a breakthrough and rapidly spread through scientific communities, McClintock admitted that many never actually understood it in the beginning. When she first presented her findings to her peers in 1951, after years of extensive research, there was dead silence, which foreshadowed the response her findings would receive for many years to follow. Despite the lackluster response to her efforts, she continued her work on corn genetics for years to come. In the 1950s, McClintock made another novel discovery about a genetic mobile element known as the Suppressor-Mutator (spm) and recognised that it could switch between an active and an inactive form.

However, in the 1960s and 1970s, other scientists began to observe the phenomenon of transposition in bacteria. When scientists Francois Jacob and Jacques Monod described genetic regulation in bacteria, Barbara quickly responded with a paper aptly titled “Some Parallels Between Gene Control Systems in Maize and in Bacteria”. Finally in 1983, 35 years after her first published report of transposition, McClintock received the Nobel Prize for Medicine, honouring her contributions to the field of genetics, namely her independent identification of genetic transposition.

McClintock received many honors and awards for her illustrious career including the National Medal of Science (1970), awarded by President Richard Nixon, the Achievement Award of the American Association of University Women (1947), the Award of Merit by the Botanical Society of America (1957), the Kimber Genetics Award from the National Academy of Sciences (1967), the National Medal of Science (1970), the Lewis S. Rosenstiel Award for Distinguished Work in Basic Medical Research (1978), the Louis and Bert Freedman Foundation Award for Research in Biochemistry (1978), the Wolf Prize in Medicine (1981), Albert Lasker Basic Medical Research Award (1981), and the Louisa Gross Horwitz Prize (1982). Additionally, she was elected to the National Academy of Sciences in 1944 at the age of 42 and elected the first woman president of the Genetics Society of America in 1945.

Barbara McClintock died at the age of 90 in Huntington, New York. Her legacy lives on through her remarkable contributions to maize cytogenetics and the field of genetics more broadly. Today, she is an inspiration to thousands of women that wish to pursue genetics and has truly proved that sometimes it takes an unconventional perspective to truly make progress in a field.

by Raina Talwar Bhatia

References

2002–2011 DNA Learning Center. (2019). Barbara McClintock :: DNA from the beginning. DNA from the Beginning — An animated primer of 75 experiments that made modern genetics. https://www.dnaftb.org/32/bio.html

2009 National Science and Technology Medals Foundation. (2012). National science & technology medals Foundation: The laureates. Wayback Machine. https://web.archive.org/web/20120911074221/https://www.nationalmedals.org/medals/1970.php

Cold Spring Harbor Laboratory. (1992). Barbara McClintock Biography. Library — Cold Spring Harbor Laboratory — Library & Archives. https://library.cshl.edu/sp/scientists/barbara_mcclintock/mcclintock_biography.html

McClintock, B. (1983). The Nobel prize in physiology or medicine 1983. NobelPrize.org. https://www.nobelprize.org/prizes/medicine/1983/mcclintock/biographical/

NLM. (2019). Biographical overview. Barbara McClintock — Profiles in Science. https://profiles.nlm.nih.gov/spotlight/ll/feature/biographical

Pearse, Y. (2018, May 11). Meet Barbara McClintock, who used corn to decipher ‘jumping genes’. Massive Science. https://massivesci.com/articles/barbara-mcclintock-nobel-corntent/

Ravindran, S. (2012, December 11). Barbara McClintock and the discovery of jumping genes. PNAS. https://www.pnas.org/content/109/50/20198

US National Library of Medicine. (2019). Education and research at Cornell, 1925–1931. Barbara McClintock — Profiles in Science. https://profiles.nlm.nih.gov/spotlight/ll/feature/cornell