Barbara McClintock (June 16, 1902 - September 2, 1992) is an American scientist and cytogeneticist who was awarded the 1983 Nobel Prize in Physiology or Medicine. McClintock received his PhD in botany from Cornell University in 1927. There he began his career as a leader in the development of corn cytogenetics, focusing his research for the rest of his life. From the late 1920s, McClintock studied chromosomes and how they changed during reproduction in corn. He developed a technique to visualize corn chromosomes and used microscopic analysis to show many fundamental genetic ideas. One such idea is the idea of ​​genetic recombination with crossings during meiosis - the mechanism by which chromosomes exchange information. He produced the first genetic map for corn, connecting chromosomal regions with physical features. He shows the role of telomere and centromere, an important chromosome region in the conservation of genetic information. He was recognized among the best in the field, awarded a prestigious scholarship, and was elected a member of the National Academy of Sciences in 1944.
During the 1940s and 1950s, McClintock invented transpositions and used them to show that genes are responsible for altering physical and deadly characteristics. He developed a theory to explain the suppression and expression of genetic information from one generation of corn crops to the next. Because of his research skepticism and its implications, he stopped publishing his data in 1953.
Later, he conducted an extensive study of the cytogenetics and ethnobotany of the South American corn race. McClintock's research became well understood in the 1960s and 1970s, when other scientists confirmed the mechanisms of genetic change and genetic regulation that he showed in his corn research in the 1940s and 1950s. The recognition and recognition of his contribution to the field followed, including the Nobel Prize in Physiology or Medicine, was awarded to him in 1983 for the discovery of genetic transposition; she is the only woman who received the Nobel Prize without sharing in that category.
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Barbara McClintock was born Eleanor McClintock on June 16, 1902 in Hartford, Connecticut, the third child of four children born to homeopathic physicians Thomas Henry McClintock and Sara Handy McClintock. Thomas McClintock was the son of an English immigrant; Sara Ryder Handy is a descendant of an old American family of Mayflower . Marjorie, the eldest, was born in October 1898; Mignon, the second daughter, was born in November 1900. The youngest, Malcolm Rider (called Tom), was born 18 months after Barbara. As a young girl, her parents decided that Eleanor, the name "feminine" and "subtle", did not suit her, and chose Barbara instead. McClintock was an independent child who started at a very young age, a trait he later identified as "the capacity to be alone". From the age of three until he started school, McClintock lived with an aunt and uncle in Brooklyn, New York to reduce the financial burden on his parents while his father established his medical practice. He is described as an only and independent child. He is close to his father, but has a difficult relationship with his mother, the tension that started when he was young.
The McClintock family moved to Brooklyn in 1908 and McClintock completed his secondary education there at Erasmus Hall High School; he graduated in early 1919. He found his love for science and reaffirmed his solitary personality during high school. He wanted to continue his studies at the Cornell University Faculty of Agriculture. His mother refused to send McClintock to college, for fear that he would not be defeated. McClintock was almost prevented from starting college, but his father intervened shortly before registration began, and he was accepted at Cornell in 1919.
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Education and research at Cornell
McClintock began his studies at Cornell's College of Agriculture in 1919. There, he participated in student governance and was invited to join the student association, although he soon realized that he preferred not joining formal organizations. Instead, McClintock takes music, especially jazz. He studied botany, receiving BSc in 1923. His interest in genetics began when he took his first course in that field in 1921. The course is based on a similar one offered at Harvard University, and taught by CB Hutchison, a crop breeder and geneticist. Hutchison was impressed by McClintock's interest, and phoned to invite him to participate in a graduate genetic course at Cornell in 1922. McClintock pointed to Hutchison's invitation as the reason he continued in genetics: "Obviously, this phone call throws dice for my future I stick with genetics thereafter. "Although it has been reported that women can not major in genetics at Cornell, and therefore MS and PhD - obtained in 1925 and 1927, respectively - are formally given in botany, recent research has revealed that women do get a bachelor's degree at Cornell's Department of Plant Breeding during that time McClintock was a student at Cornell.
During graduate study and postgraduate appointment as a botanical instructor, McClintock was instrumental in assembling a group that studied the new field of cytogenetics in corn. The group brings together plant breeders and cytologists, and includes Marcus Rhoades, candidate for Nobel laureate George Beadle, and Harriet Creighton. Rollins A. Emerson, head of the Department of Plant Breeding, supports this effort, even though he is not a cytologist himself.
He also worked as a research assistant for Lowell Fitz Randolph and later for Lester W. Sharp, both Cornell Botanists.
McClintock's cytogenetic research focuses on developing ways to visualize and characterize corn chromosomes. Certain parts of his work affect the generation of students, because it is included in most textbooks. He also developed techniques using carmine staining to visualize corn chromosomes, and showed for the first time the morphology of 10 corn chromosomes. This discovery was made because he observed cells from microspores as opposed to the tip of the root. By studying the morphology of chromosomes, McClintock is able to connect certain groups of chromosomal properties that are inherited together. Marcus Rhoades notes that McClintock's 1929 Genetic paper on the characterization of triploid corn chromosomes sparked a scientific interest in corn cytogenetics, and is associated with 10 of 17 significant advances in fields made by Cornell scientists between 1929 and 1935.
In 1930, McClintock was the first to describe a homologous chromosomal cross-interaction during meiosis. The following year, McClintock and Creighton proved the relationship between crossover chromosomes during meiosis and recombination of genetic traits. They observed how the recombination of chromosomes seen under a microscope correlated with new properties. Up to this point, it is only hypothesized that genetic recombination can occur during meiosis, although it has not been genetically proven. McClintock published the first genetic map for maize in 1931, showing the sequence of three genes on a corn chromosome 9. This information provides the data needed for the cross-over study he published with Creighton; they also show that crosses occur in sister chromatids as well as homologous chromosomes. In 1938, he produced cytogenetic centromere analysis, describing the organization and function of the centromere, as well as the fact that it can divide.
McClintock's breakthrough publications, and support from his colleagues, led to him being awarded several postdoctoral fellowships from the National Research Council. This funding enabled him to continue studying genetics at Cornell, the University of Missouri, and the California Institute of Technology, where he worked with E. G. Anderson. During the summer of 1931 and 1932, he worked in Missouri with geneticist Lewis Stadler, who introduced him to the use of X-rays as a mutagen. X-ray exposure can increase the rate of mutation above the natural background level, making it a powerful research tool for genetics. Through her work with X-ray-mutagenized corn, she identifies the chromosomal ring, which is formed when the fuse ends of a single chromosome together after radiation damage. From this evidence, McClintock hypothesized that there should be a structure at the end of the chromosome that would normally ensure stability. He pointed out that the loss of the chromosomes in meiosis causes a discoloration of the corn foliage in generations after irradiation resulting from chromosome removal. During this period, he demonstrated the existence of a region of a nucleolus organ in an area on a 6th chromosome of corn, which is necessary for nucleolus assembly. In 1933, he determined that cells could be damaged when nonhomologous recombination occurred. During the same period, McClintock hypothesized that the tip of the chromosome is protected by telomeres.
McClintock received a fellowship from the Guggenheim Foundation which allowed six months of training in Germany during 1933 and 1934. He had planned to work with Curt Stern, who had shown crossing-over in Drosophila just weeks after McClintock and Creighton had do it; However, Stern emigrated to the United States. Instead, he worked with geneticist Richard B. Goldschmidt, who was the head of the Kaiser Wilhelm Institute. He left Germany early amid rising political tensions in Europe, and returned to Cornell, remaining there until 1936, when he received an Assistant Professor offered to him by Lewis Stadler in the Department of Botany at the University of Missouri-Columbia. While still at Cornell, he was supported by a two-year Rockefeller Foundation grant obtained to him through Emerson's efforts.
University of Missouri
During his time in Missouri, McClintock expanded his research into the effects of X-rays on corn cytogenetics. McClintock observed chromosomal damage and fusion in irradiated corn cells. He was also able to show that, in some plants, spontaneous chromosomal damage occurs in endosperm cells. During the course of mitosis, he observes that the damaged ends of chromatids recombine after chromosomal replication. In mitotic anaphase, the damaged chromosome forms a chromatid bridge, which is damaged when the chromatids move toward the cell pole. The fractured end joins again in subsequent mitotic interphase, and the cycle is repeated, causing massive mutations, which can be detected as variations in the endosperm. The reupting-rejoining-bridge cycle is a key cytogenetic discovery for several reasons. First, it shows that chromosome joining is not a random occurrence, and second, it shows a large-scale mutation source. For this reason, it remains an area of ​​interest in cancer research today.
Although his research flourished in Missouri, McClintock was not satisfied with his position at the University. He remembered being expelled from the faculty meeting, and was unaware of the positions available at other institutions. In 1940, he wrote to Charles Burnham, "I have decided that I should look for another job." As far as I can see, there is no more for me here.I am an assistant professor at $ 3,000 and I feel confident that is the limit for me. "Initially, McClintock's position was created specifically for him by Stadler, and may depend on his presence at the university. McClintock believes he will not get a tenure in Missouri, although according to some accounts, he knows he will be offered promotions from Missouri in the spring of 1942. Recent evidence suggests that McClintock is more likely to decide to leave Missouri because he has lost the trust of his employer and in administration University, after learning that his work would be threatened if Stadler went to Caltech, as he did. The university's revenge on Stadler strengthens his sentiment.
In early 1941, he took a leave of absence from Missouri hoping to find a position elsewhere. He received a Professorship visit at Columbia University, where his former Cornell colleague Marcus Rhoades was a professor. Rhoades also offers to share his research field at Cold Spring Harbor on Long Island. In December 1941, he was offered a research position by Milislav Demerec, the newly appointed acting director of the Carnegie Institute of Cold Spring Harbor Genetics Laboratory in Washington; McClintock accepted his invitation regardless of his doubt and became a regular member of the faculty.
Cold Spring Harbor
After a temporary appointment for a year, McClintock received a full-time research position at Cold Spring Harbor Laboratory. There, he is very productive and continues his work with a fusion-bridge fusion cycle, using it to replace X-rays as a tool for mapping new genes. In 1944, in recognition of his superiority in the field of genetics during this period, McClintock was elected to the National Academy of Sciences - only the third woman chosen. That same year, she became the first female president of the Genetics Society of America; he was elected vice president in 1939. In 1944 he conducted a cytogenetic analysis of Neurospora crassa at the suggestion of George Beadle, who used mushrooms to denote a single enzyme-gene link. He invited her to Stanford to do some research. He succeeds in describing the number of chromosomes, or karyotypes, of N. crassa and describes the entire species life cycle. Beadle says "Barbara, in two months at Stanford, is doing more to clear the cytology of Neurospora than all other cytological genetics that have been done at all times before in all forms of fungus." N. crassa has been a model species for classical genetic analysis.
Discovery of control elements
In the summer of 1944 at Cold Spring Harbor Laboratory, McClintock began a systematic study of the mosaic patterns of mosaic seed patterns of corn and the unstable legacy of this mosaic. He identified two dominant and interacting genetic loci he named Ds Dissociation Ds and Activator ( Ac ). He found that
He observed the effects of the transposition of Ac and Ds by changes in the pattern of staining in the corn seed of the controlled generations of the crosses, and illustrates the relationship between the two loci via complicated microscopic analysis. He concluded that Ac controls the transposition of Ds from chromosome 9, and that the motion of Ds is accompanied by chromosomal damage. When Ds moves, the aleurone color gene is released from the pressing effect of Ds and changes to the active form, which initiates the synthesis of pigments in the cell. The transposition of Ds in different cells is random, may move in some but not the other, causing the color mosaic. The size of the colored spot on the seed is determined by the stage of seed development during the dissociation. McClintock also found that transposition Ds is determined by the number of Ac copies in the cell.
Between 1948 and 1950, he developed a theory by which these mobile elements regulate genes by inhibiting or modulating their actions. He refers to the Dissociation and Activator as "controlling units" - then, as "controlling elements" - to distinguish them from genes. He hypothesizes that gene regulation can explain how complex multicellular organisms made from cells with identical genomes have cells with different functions. McClintock's discovery challenged the concept of genome as a set of static instructions passed between generations. In 1950, he reported his work on Ac/Ds and his ideas about gene regulation in a paper entitled "The origin and behavior of locus that may change in corn" published in the journal Proceedings of the National Academy of Sciences Knowledge . In the summer of 1951, he reported his work on the origin and behavior of a mutable locus in corn at the annual symposium at Cold Spring Harbor Laboratory, which presents papers with the same name. This paper investigates the instability caused by Ds and Ac or just Ac in four genes, along with the tendency of the genes to unexpectedly back to the wild phenotype. He also identifies the "family" transposon, which does not interact with each other.
His work on controlling gene elements and regulation is conceptually difficult and not immediately understood or accepted by his contemporaries; he describes his acceptance of research as "confusion, even hostility". However, McClintock continues to develop his ideas about controlling the elements. He published a paper in Genetics in 1953, where he presented all of his statistical data, and toured university lectures throughout the 1950s to talk about his work. He continues to investigate the problem and identifies a new element he calls Splitter ( Spm ), which, although similar to Ac/Ds , acts in a way more complex. Like Ac/Ds , some versions can transpose itself and some can not; unlike Ac/Ds , at present, it completely suppresses the expression of mutant genes when they are usually not completely suppressed. Based on other scientists' reaction to his work, McClintock feels he is at risk of alienating the mainstream of science, and from 1953 stopped publishing his research reports on controlling elements.
The origin of corn
In 1957, McClintock received funding from the National Academy of Sciences to begin research on the original types of maize in Central America and South America. He was interested in studying the evolution of maize through chromosomal changes, and being in South America would allow him to work on a larger scale. McClintock explores the characteristics of chromosomes, morphology, and the evolution of various races of maize. After extensive work in the 1960s and 1970s, McClintock and his collaborators published a seminal study of the Chromosome Constitution on the Race of Corn, leaving their mark on paleobotany, ethnobotany, and evolutionary biology.
Reinvent
McClintock officially retired from his position at the Carnegie Institution in 1967, and was appointed a Distinguished Service Member of the Carnegie Institution of Washington. This honor enabled him to continue working with graduate students and colleagues at the Cold Spring Harbor Laboratory as an emeritus scientist; he lives in the city. In connection with his decision 20 years earlier to stop publishing his detailed account of his work on the controlling element, he wrote in 1973:
Over the years I have found that it is difficult if it is impossible to bring another's consciousness to the nature of its tacit assumption when, by some special experience, I have been made aware of it. It became very clear to me in my attempts during the 1950s to convince geneticists that gene action should be and is controlled. It is now equally painful to recognize the assumptions that many people hold to the nature of the controlling elements in corn and their operating behavior. Someone must wait for the right time for conceptual change.
The significance of McClintock's contributions was revealed in the 1960s, when the work of the French geneticist Francois Jacob and Jacques Monod described the genetic regulation of the lac operon , a concept he showed with Ac/Ds at 1951. After Jacob and Monod's 1961
McClintock is widely credited with finding transpositions after other researchers finally found the process on bacteria, yeast, and bacteriophage in the late 1960s and early 1970s. During this period, molecular biology has developed significant new technology, and scientists were able to demonstrate the molecular basis for transposition. In the 1970s, Ac and Ds were cloned by other scientists and proved to be Class II transposons. Ac is a complete transposon that can produce functional transposes, which are necessary for elements to move within the genome. Ds has a mutation in the transposase gene, which means it can not move without another source of transposase. So, as McClintock observed, Ds can not move in the absence of Ac . Spm has also been characterized as transposon. Subsequent research has shown that transposons are usually immobile unless the cells are placed under pressure, such as by irradiation or bridge-fusion dams, and thus their activation during stress can serve as a source of genetic variation for evolution. McClintock understands the role of transposons in evolution and genomic change well before other researchers understand the concept. Currently, Ac/Ds is used as a tool in plant biology to produce mutant plants used for characterizing gene function.
Awards and acknowledgments
In 1947, McClintock received an Achievement Award from the American Association of University Women. He was elected Fellow of the American Academy of Arts and Sciences in 1959. In 1967, McClintock was awarded the Kimber Genetics Award; three years later, he was given the National Medal of Science by Richard Nixon in 1970. He was the first woman to be awarded the National Medal of Science. Cold Spring Harbor named a building in his honor in 1973. He received the Louis Award and Bert Freedman Foundation and Lewis S. Rosensteil Awards in 1978. In 1981, he became the first recipient of the MacArthur Grant Foundation, and was awarded the Albert Lasker Award for Research Basic Medical, Wolves Prize in Medicine, and Thomas Hunt Morgan Medal by the Genetics Society of America. In 1982, he was awarded Louisa Gross Horwitz of Columbia University for his research in "the evolution of genetic information and its expression control."
In particular, he received the Nobel Prize for Physiology or Medicine in 1983, the first woman to win the prize was not shared, credited by the Nobel Foundation for discovering "moving genetic elements"; it was over 30 years after he initially described the phenomenon of the controlling element. He was compared to Gregor Mendel in terms of his scientific career by the Swedish Academy of Sciences when he was awarded the Prize.
He was elected a Foreign Member of the Royal Society (ForMemRS) in 1989. McClintock received the Benjamin Franklin Medal for Distinguished Achievement in the Science of the American Philosophical Society in 1993. He was awarded 14 Honorary Doctor of Science and Honorary Doctor of Human Letters. In 1986 he was inducted into the National Women's Hall of Fame. During his final years, McClintock underwent a more open life, especially after the 1983 Evelyn Fox Keller biography of him, A Feeling for the Organism, brought McClintock's story to the public. He remains regularly present in the Cold Spring Harbor community, and gives lectures on the elements of mobile genetics and the history of genetic research for the benefit of junior scientists. An anthology of his 43 publications Discovery and Characterization of Transposable Elements: The Collected Papers of Barbara McClintock was published in 1987.
The McClintock Prize is named in his honor. The award winners include David Baulcombe, Detlef Weigel Robert A. Martienssen, Jeffrey D. Palmer and Susan R. Wessler.
Next year
McClintock spent years later, posting the Nobel Prize, as a key leader and field researcher at Cold Spring Harbor Laboratory in Long Island, New York. McClintock died of natural causes in Huntington, New York, on September 2, 1992 at the age of 90; he never married or had children.
Legacy
Since his death, McClintock has been the subject of biography by science historian Nathaniel C. Comfort's The Tangled Field: Barbara McClintock's Search for the Genetic Control Pattern . The contest biography comforts several claims about McClintock, described as the "McClintock Myth", which he claims was immortalized by Keller's earlier biography. Keller's thesis is that McClintock has long been ignored or ridiculed because he is a woman who works in the field of science. For example, when McClintock presented his findings that the genetics of maize were incompatible with Mendelian distribution, geneticist Sewall Wright expressed confidence that he did not understand the underlying mathematics of his work, the belief he expressed against other women at the time. In addition, geneticist Lotte Auerbach recounts that Joshua Lederberg returned from a visit to the McClintock lab with the statement: 'For God's sake, the woman is mad or genius.' "As Auerbach put it, McClintock has thrown Lederberg and his comrades after half an hour 'because of their arrogance.He can not stand the arrogance... He feels he has crossed the desert alone and no one follows him.'"
Comfort, however, confirms that McClintock is highly respected by his professional counterparts, even in his early years. Although Comfort argues that McClintock is not a victim of gender discrimination, he has been widely written in the context of women's studies. Recent biographical works on women in science showcase their experiences. She was appointed as a role model for girls in children's literature such as Edith Hope Fine Barbara McClintock, Genetic Nobel Prize , Deborah Heiligman Barbara McClintock: Alone in Her Field. and Mary Kittredge Barbara McClintock . The latest biography for young adults by Naomi Pasachoff, Barbara McClintock, Genius of Genetics, provides a new perspective, based on the current literature.
On May 4, 2005, the United States Postal Service issued an American Scientists "warning stamp series, a set of four self-adhesive pegs of 37 cents in several configurations. The scientists depicted are Barbara McClintock, John von Neumann, Josiah Willard Gibbs, and Richard Feynman. McClintock is also featured in a 1989 four-cap edition from Sweden that illustrates the work of eight Nobel Prize-winning geneticists. A small building at Cornell University and a laboratory building at the Cold Spring Harbor Laboratory was named for him. A street has been named after him at the new Adlershof Development Society's Berlin park.
Some of McClintock's personality and scientific achievements are referred to in Jeffrey Eugenides novel in 2011 The Marriage Plot, which tells the story of a yeast geneticist Leonard who suffers from bipolar disorder. He worked in the laboratory loosely based on Cold Spring Harbor. Character that reminds McClintock is a closed geneticist in a fictitious laboratory, who makes the same discovery as his factual counterpart.
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