Barbara McClintock

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Barbara McClintock (June 16, 1902-1992), an American scientist and cytogeneticist who was awarded the 1983 Nobel Prize in Physiology or Medicine, was a recipient of the Physiology or Medicine honor.

In 1927, McClintock earned her PhD in botany from Cornell University.

She began her career as the leader in the field of maize cytogenetics, but the subject of her study for the remainder of her life was not limited.

McClintock analyzed chromosomes and how they change during maize reproduction.

She invented the method for visualizing maize chromosomes and used microscopic analysis to explore many basic genetic theories.

One of those theories was the possibility of genetic recombination during meiosis, which is a process by which chromosomes exchange information.

She created the first genetic map for maize, comparing regions of the chromosome to physical characteristics.

She discussed the role of the telomere and centromere, two chromosome regions that are crucial in genetic research conservation.

She was named one of the best in the field, received prestigious fellowships, and elected a member of the National Academy of Sciences in 1944. McClintock demonstrated transposition and showed that genes were responsible for changing physical appearances both in the 1940s and 1950s.

She developed theories to explain the denial and dissemination of genetic information from one generation of maize plants to the next.

She stopped publishing her results in 1953 due to skepticism about her study and its implications. She completed an extensive research into the cytogenetics and ethnobotany of maize races from South America later.

McClintock's study became well known in the 1960s and 1970s, as other scientists outlined the mechanisms of genetic change and gene regulation, which she had observed in her maize studies in the 1940s and 1950s.

She has been rewarded with awards and accolades for her contributions to the field, as well as the Nobel Prize in Physiology or Medicine, which was given to her in 1983 for the discovery of genetic transposition; she is the only woman to receive an unshared Nobel Prize in this category.

Early life

Barbara McClintock was born in Hartford, Connecticut, on June 16, 1902. She was the third of four children born to homeopathic physician Thomas Henry McClintock and Sara Handy McClintock. Thomas McClintock was the son of a British immigrant; Sara Ryder Handy descended from an old Mayflower family in the United States. Marjorie, the oldest child, was born in October 1898; Mignon, the second daughter, was born in November 1900. Malcolm Rider (called Tom) was born 18 months after Barbara's birth and is the youngest. Eleanor, a "feminine" and "delicate" name, was not appropriate for her, so she chose Barbara instead. McClintock was a young girl who began to be independent, a characteristic she later described as her "capacity to be alone." McClintock lived with an aunt and uncle in Brooklyn, New York, from the age of three to school in order to lessen the financial burden on her parents while her father began his medical practice. She was described as a solitary and independent child. She was close to her father, but she had a difficult relationship with her mother, which began when she was young.

The McClintock family immigrated to Brooklyn in 1908, but McClintock completed her secondary education at Erasmus Hall High School in 1919; she graduated early in 1919. During high school, she discovered her love of science and reaffirmed her solitary personality. She wanted to continue her studies at Cornell University's College of Agriculture. McClintock's mother refused to send her child to college due to a fear that she would be unmarriageable, which was a common reaction at the time. McClintock was almost refused to enroll in college, but her father allowed her to start only after registration was started, and she matriculated at Cornell in 1919.

Education and research at Cornell

McClintock began her studies at Cornell's College of Agriculture in 1919. She spent time in student government and was invited to join a sorority, but she soon discovered that she did not want to join formal organisations. Rather, McClintock took up jazz, specifically jazz. She studied botany after receiving a BSc in 1923. When she took her first course in 1921, she began her interest in genetics. The course was based on a similar one at Harvard University and was taught by C. B. Hutchison, a plant breeder and geneticist. Hutchison was captivated by McClintock's passion and called upon to enroll in Cornell's graduate genetics program in 1922. McClintock referred to Hutchison's invitation as a catalyst for her interest in genetics: "Obviously, this phone call sparked the death for me." "I stayed with genetics until the time." Although it has been reported that women did not pursue genetics at Cornell, and hence her MS and PhD degrees in botany, which were awarded in 1925 and 1927 respectively, have been found to graduate degrees in Cornell's Plant Breeding Department during the time McClintock was a Cornell undergraduate.

McClintock was instrumental in assembling a team that looked at the emerging field of cytogenetics in maize during her graduate studies and postgraduate work as a botany instructor. Marcus Rhoades, future Nobel Laureate George Beadle, and Harriet Creighton brought together plant breeders and cytologists, as part of this group. Rollins A. Emerson, the Plant Breeding Department's chief, approved these efforts, though he was not a cytologist himself.

She worked as a research assistant for Lowell Fitz Randolph and then for Lester W. Sharp, both Cornell botanists.

McClintock's cytogenetic research concentrated on the discovery of ways to measure and characterize maize chromosomes. Since it was included in most textbooks, this particular portion of her research inspired a generation of students. She also developed a device using carmine staining to visualize maize chromosomes, and she displayed the morphology of the 10 maize chromosomes for the first time. This discovery was made because she observed cells from the microspore rather than the root tip. McClintock was able to identify specific chromosome groups of traits that were related to certain chromosome groups of genes that were inherited together by studying the morphology of the chromosomes. Marcus Rhoades said McClintock's 1929 Genetics paper on the characterization of triploid maize chromosomes sparked scientific curiosity in maize cytogenetics, and she attributed to her 10 of the field's top tenths in the field that were made by Cornell scientists between 1929 and 1935.

McClintock was the first person to describe the interplay of homologous chromosomes during meiosis in 1930. McClintock and Creighton established the connection between chromosomal transfer during meiosis and genetic mutation recombination. They investigated how the recombination of chromosomes seen under microscope corresponded to novel features. It had only been assumed that genetic recombination would occur during meiosis before this point, but it had not been demonstrated genetically. In 1931, McClintock published the first genetic map for maize, displaying the order of three genes on maize chromosome 9. This information was essential for Creighton's cross-over study, which revealed that crossing-over occurs in sister chromatids as well as homologous chromosomes. She published a cytogenetic analysis of the centromere in 1938, describing the centromere's structure and function as well as the fact that it can divide.

McClintock's pioneering research and encouragement from her coworkers resulted in her being given several postdoctoral fellowships from the National Research Council. With this support, she was able to continue to study genetics at Cornell University of Missouri and the California Institute of Technology, where she worked with E. G. Anderson. She worked at the University of Missouri with geneticist Lewis Stadler, who introduced her to the use of X-rays as a mutagen during 1931 and 1932. Exposure to X-rays can raise the rate of mutation above the normal background level, making it a popular research tool for genetics. Ring chromosomes, which occur when the ends of a single chromosome fuse together after radiation damage, are discovered by X-ray-mutagenized maize. McClintock hypothesized that there must be a structure on the chromosome tip that would normally guarantee stability from this evidence. Following to irradiation resulting from chromosomal deletion, she demonstrated that the absence of ring-chromosomes at meiosis resulted in variegation in maize foliage in generations subsequent to irradiation. During this time, she displayed the presence of the nucleolus organ region in a region on maize chromosome 6, which is required for the assembly of nucleolus nucleolus. She demonstrated in 1933 that cells can be destroyed if nonhomologous recombination occurs. McClintock hypothesized that telomeres covered the tips of chromosomes.

McClintock was given a fellowship from the Guggenheim Foundation, which provided for six months of instruction in Germany between 1933 and 1934. She had intended to work with Curt Stern, who had performed crossing-over in Drosophila just weeks before McClintock and Creighton had done so; however, Stern emigrated to the United States. Rather, she worked with geneticist Richard B. Goldschmidt, who was a director of Berlin's Kaiser Wilhelm Institute for Biology. She left Germany early in Europe's rising political tensions and returned to Cornell, where she stayed there until 1936, when Lewis Stadler, a University of Missouri researcher, accepted an Assistant Professorship. She was aided by a two-year Rockefeller Foundation grant that was awarded to her by Emerson's efforts while still attending Cornell.

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