I never thought of stopping
and I just hated sleeping.
I can't imagine having a better life.

-- Barbara McClintock

At a time when women were largely excluded from the sciences, Barbara McClintock (1902-1992) made some fundamental discoveries in the field of genetics. She was rewarded for the discovery of transposable genetic elements with the 1983 Nobel Prize, thirty-five years after the publication of her work. She singlehandedly turned the field of genetics on its ear, not only from the perspective of social and gender equality, but from a scientific standpoint.

Early Life

Barbara McClintock was born in 1902 in Hartford, Connecticut, but she grew up in Brooklyn, New York, attending Erasmus Hall High School there from 1915 to 1919. She was an excellent student and was accepted into Cornell University in 1919. During her studies there, in 1921, she attended the only course in genetics open to undergraduate students. It was as if a light bulb went off in McClintock's head.

Seeing her deep interest in the topic, C. B. Hutchison, the teacher of the course, invited Barbara to participate in the only other genetics course offered at Cornell in 1922, a graduate course. At the same time, she took coursework in cytology and learned of the general structure and form of chromosomes, about which little was known at the time.

She stayed at Cornell (with short stints with the National Research Council and Guggenheim Foundation from 1931 to 1934) until 1936, earning her BS in botany in 1923 and her Ph.D. in genetics in 1927 and became engrossed in the developing field of genetics, much of which centered around Cornell. During that time, she began to focus on maize, mostly because of its agronomic importance. In one particularly important study, she, along with Harriet Creighton, demonstrated the principle of genetic crossing over was actually a physical process, already known as chiasmata. The connection between these events would lead McClintock's research for years to come.

In 1936, she moved to the University of Missouri at the encouragement of Lewis Stadler, one of the top geneticists in the world. Missouri was the center of maize research in the world at the time (and is still one of the top places). Here, she focused on the discovery of the telomere, which is the tip of a chromosome that maintains structural stability. This led into her deep interest in chromosomal breakage that would fuel her research for the remaining years. She began to study a particular type of breakage called the breakage-fusion bridge.

Due to internal politics, it became apparent that McClintock would not receive a tenured position at Missouri, so in 1941, she moved on to Cold Spring Harbor, New York and the laboratory there. Shortly after moving, she was awarded a tenured position and membership in the National Academy of Sciences (1944) for her work on telomere research. She also served as president of the American Genetics Society in 1945.

Major Discovery

In 1944, McClintock began to uncover what would be the major discovery of her life. While continuing to investigate the breakage-fusion bridge, she began to notice some seemingly inexplicable anomalies in her data. Certain mutable genes appeared to be transferred from cell to cell during development of the corn kernel. In her later words, "one cell gained what the other cell lost." This discovery of transposable elements is a landmark moment in the evolution of genetics, right up there with the discovery of the double helix by Watson and Crick.

McClintock carefully studied this phenomenon for six years, not actually publishing any reports on the subject until very late in 1950. Her first public presentation of her work on transposable elements occurred in early 1951 at the Cold Spring Harbor Symposium, a gathering of geneticists from around the world. Her presentation was met with stunned silence from a virtual who's who of genetics at the time.

The six years of strong observation and persistence are what carried the day for McClintock. With her conclusion supported by a tremendous volume of data, it became clear that even though her conclusion was very much against the grain of modern thinking in genetics at the time, she was right. Her work was heavily derided at first, but over time her work gradually came to be accepted in the field and is now viewed as a landmark body of work.

Throughout the 1950s and 1960s, molecular techniques were developed that allowed the biochemical verification of McClintock's much earlier genetics-based work.

Later Years

In the 1960s and 1970s, McClintock would go on to make yet another major contribution to the study of maize. She became interested in looking at the evolution of maize from its earlier relatives, especially teosinte and its close cousin, sorghum. In studying this, McClintock spent much of the 1970s in South America, investigating the different strains of maize found throughout the Americas. This was one of the founding works in the study of evolutionary genetics and largely founded the field of ethnobotany.

It was during the late 1960s that McClintock's major contributions to genetics began to be widely recognized. She was awarded the Kimber Medal in 1967, the National Medal of Science in 1970, and the Lasker Award in 1981. She was also made a member of the National Women's Hall of Fame. But the culmination of all of her work came in 1983, when she was awarded the Nobel Prize in Physiology or Medicine alone for her work on the discovery of transposable elements.

McClintock retired in 1981 and drifted quietly through the 1980s, appearing at scientific meetings and other such events with her usual quiet demeanor. She passed away in 1992, leaving behind a great legacy of science and a major advancement in our knowledge of maize and other organisms.

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