Barbara McClintock

Geneticist

• Born: June 16, 1902
• Birthplace: Hartford, Connecticut
• Died: September 2, 1992
• Place of death: Huntington, Long Island, New York

American geneticist

A pioneer in classical and molecular genetics, McClintock won the Nobel Prize in Physiology or Medicine in 1983. Her theories that patterns of genetic traits caused by mutations do not follow the accepted rules of genetics, and that sections of chromosomes detach and move to a new location during development, were far ahead of contemporary genetic research.

Born: June 16, 1902; Hartford, Connecticut

Died: September 2, 1992; Huntington, New York

Primary field: Biology

Specialty: Genetics

Early Life

Barbara McClintock was the third daughter of Sara Handy and Thomas Henry McClintock. Shortly after their marriage, Thomas McClintock finished medical school at Boston University, and after a few relocations, the couple moved to Hartford, Connecticut, where Barbara was born. Less than two years after McClintock’s birth, her younger brother Malcolm was born. McClintock’s mother, unable to cope with four small children and financial issues, decided to send McClintock to live with her aunt and uncle in Massachusetts. McClintock came back to her parents’ house when it was time for her to start school. In the interim, the McClintocks had moved to the Flatbush section of Brooklyn, New York, which in those days was a semirural area.

In high school, McClintock discovered science. She loved information and problem solving. Her mother began to worry that McClintock would pursue knowledge to the detriment of her “feminine development” and tried to dissuade her, but McClintock was set on attending Cornell University, a school that was known for accepting and supporting the education of women.

Beginning her studies at Cornell in 1919, McClintock soon blossomed both intellectually and socially. Elected president of the women’s freshman class, she began to date, played banjo in local cafes, and managed a heavy class schedule. After a couple of years, however, she began to be disillusioned with the social whirl. Devoting more and more time to academics, she was allowed to take a graduate class in genetics during her junior year, and her lifelong fascination with the subject began.

Life’s Work

At the time of McClintock’s matriculation at Cornell, genetics was a new science, scarcely more than a few decades old. Cytology (the branch of biology that concerns cells) was relatively new, and many cellular structures were still a mystery. Evolutionary biologist Thomas Hunt Morgan, working with Drosophila (fruit flies) at Columbia, had proposed that genes were located on the chromosomes like beads on a string, but many scientists did not accept that idea.

McClintock started her career with the successful identification of maize (Indian corn) chromosomes, distinguishing the ten individual chromosomes that constitute each individual kernel. After completing her bachelor’s degree, McClintock began graduate work in the Botany Department; the Department of Plant Breeding, which included genetics, did not accept women as graduate students. She received her doctorate in 1927, when she was twenty-four. Fascinated by the work being done by Morgan and others, she stayed on at Cornell to try to parallel Morgan’s Drosophila work with maize. Two other researchers who came to Cornell at this time were Marcus Rhodes and George Wells Beadle, both of whom later became prominent geneticists. In this environment, McClintock’s research thrived. By 1931, she had published nine papers on maize chromosomal morphology and attracted renown within her field.

During these years, Harriet Creighton, a new graduate student, arrived at Cornell. McClintock convinced her to enroll as a cytology and genetics major, after which Creighton began working as McClintock’s assistant. Toward the end of the first year, McClintock suggested that Creighton attempt to prove the commonly assumed correlation between chromosomal crossover (an actual physical exchange of chromatids during meiosis) and genetic crossover (an organism’s display of a combination of parental traits that are normally linked). McClintock believed that this could be proved through a series of experiments involving a particular maize chromosome, and she had identified and isolated kernels that involved the traits needed. Creighton and McClintock worked on the problem until the spring of 1931, when, at the urging of Morgan, they published their successful results. It became a landmark essay in classical genetics.

As faculty positions were simply not open to women at Cornell, McClintock decided to leave. For a number of years, McClintock moved between Cornell, the California Institute of Technology, and the University of Missouri, where with Lewis Stadler she was researching the existence of ring chromosomes. In 1933, McClintock received a fellowship to go to Germany and work with the famous geneticist Richard B. Goldschmidt. She found the reality of Nazi Germany unbearable and returned within the year. In 1935, Stadler convinced the University of Missouri to offer McClintock a position as assistant professor, which she accepted. Her unconventional ways and outspokenness did not fit in well at Missouri, and while her research went well, she was passed over for promotion in favor of men whose credentials were far less impressive. In 1941, she relocated to the Carnegie Institute of Washington at Cold Spring Harbor, New York.

In 1944, the National Academy of Sciences elected McClintock to its membership. She was only the third woman to receive this honor. Between 1944 and 1951, McClintock studied patterns of genetic traits caused by mutations, traits that did not seem to follow the accepted rules of genetics. These traits did seem to occur with some regularity, however, implying that some form of controlling factors were involved. McClintock proposed that, at some point during development, sections of chromosomes actually detached and moved to a new location, contrary to Morgan’s “beads on a string” concept. Furthermore, these transpositions seemed to be controlled by a factor on the chromosome itself. In 1951, she presented her findings at the annual Cold Spring Harbor Symposium. While her work received a cool reception in the scientific community, Jacques Monod and François Jacob published a paper that confirmed some of her findings in 1961. McClintock immediately submitted an article for publication and presented another at Cold Spring Harbor, but still her work was not accepted.

In the mid-1960s, McClintock’s situation began to improve. She received the Kimber Genetics Award in 1967 and the National Medal of Science in 1970, as more of her findings were confirmed by other researchers and studies again started citing her work. This trend continued in the 1970s, and McClintock started publishing again. She gained new prominence, winning awards and prizes that brought her prestige and money. She won the Nobel Prize in Physiology or Medicine in 1983, becoming the first woman to win an unshared Nobel Prize in this category and the third woman to do so in any science category.

Still at Cold Spring Harbor, McClintock continued her research, maintaining her independence and isolation despite the belated acceptance of her work. In later years, she studied Tibetan Buddhism and biofeedback techniques, which fascinated her in their incorporation of the same holistic approach she had brought to the study of maize for so many years. McClintock died on September 2, 1992, at the age of ninety.

Impact

McClintock’s work was influential in the field of genetics. Her discoveries on the behavior of chromosomes during genetic transposition earned her the Nobel Prize for Physiology or Medicine in 1983. Her research on the incidence and distribution of chromosomal features and abnormalities helped account for the evolution of the varieties of corn crops.

Throughout her life, McClintock wanted gender to be disregarded in assessments of a scientist’s worth. She wanted to be accepted and respected on her own merit, as a researcher and expert in her field. She confronted and overcome many barriers throughout her career. Others followed her example. Geneticist Evelyn Witkin, for example, established the Barbara McClintock Chair at Rutgers University to acknowledge the enormous debt she owed McClintock for her inspiration and encouragement in their ten years together at Cold Spring Harbor. Creighton, who owed the inception of her career to McClintock, commented, “It was the best steering anyone could have given me.” McClintock paved a path that continues to be followed by many scientists, both men and women. Her complete dedication and unique vision serve as an example to women in every field.

Bibliography

Bennetzen, Jeff L., and Sarah C. Hake. Handbook of Maize: Genetics and Genomics. New York: Springer, 2009. Print. Examines maize as a significant food and fuel crop and a subject for scientific research. Includes a chapter devoted to McClintock’s research.

Comfort, Nathaniel C. The Tangled Field: Barbara McClintock’s Search for the Patterns of Genetic Control. Cambridge, Mass.: Harvard UP, 2001. Print. Examines biographer Evelyn Fox Keller’s depiction of McClintock’s milieu and McClintock’s own description of her role in science. Maintains that McClintock was always a respected scientist and a distinguished figure.

Cullen, J. Heather. Barbara McClintock. New York: Chelsea House, 2003. Print. Chronicles McClintock’s life and career. Appropriate for high-school-level readers.

Fedoroff, Nina, and David Botstein, eds. The Dynamic Genome. Cold Spring Harbor: Cold Spring Harbor Laboratory P, 1992. Print. A collection of essays written as tributes and remembrances for McClintock’s ninetieth birthday. Includes technical articles on genetics and McClintock’s impact, as well as reprints of four of McClintock’s most influential articles.

Lewin, Roger. “A Naturalist of the Genome.” Science 222 (28 Oct. 1983): 402–405. Print. Published shortly after McClintock received the Nobel Prize. Includes a concise and clear overview of the work for which the prize was awarded as well as some discussion of where McClintock’s discoveries have led since.