Barbara McClintock

Barbara McClintock (June 16th 1902 - September 2nd 1992) is a scientist American, regarded as one of most eminent the cytogeneticians of the world.

She supported in 1927 a thesis of doctorate in Botanique with the Université Cornell where she had undertaken pointed research on the Cytogénétique of the corn, which will remain besides its field of predilection during all its career.

At the end of the years 1920, she studied the Chromosome S and their modifications during the reproduction at corn. Its work and its results were astonishing and very advances some over the time: it developed techniques to observe the chromosomes of corn and used analyzes made with the Microscope to show many fundamental genetic theories, of which that concerning the genetic exchange of information by the chromosomes by Crossing-over during the Méiose. It produced the first Genetic card corn, linking the chromosomal regions with physical features and showed the role of the Télomère and the Centromère, two important areas of the chromosomes in the conservation of genetic information. She was recognized like one of best of her field, gaining prestigious price and being elected with the National Academy off Sciences in 1944. She accepted the Nobel Prize of medicine in 1983 for her discovery of the mobile genetic factors called Transposon S.

During the decades 1940 and 1950, McClintock discovered the transposition and used it to show how the Gène S are responsible for the activation or not of physical characteristics. It developed theories explaining the repression or the genetic expression of information transmitted of a generation of corn to the other. Meeting skepticism on its research and its implications, it stopped the publication of its results in 1953. Later, she studied the cytogenetics and the éthnobotanique one of the Race of corn of South America. Its research becomes better understood in the years 1960 and 1970, whereas researchers show the genetic mechanisms and the genic Régulation, that it had previously found. She accepted many prices recognizing her scientific contribution, whose Nobel Prize of medicine in 1983 for its discovery of the Transposon S. To date, she is the first and the only woman individually to receive a Nobel Prize in this category.

Biography

Barbara McClintock was born with Hartford (Connecticut), the third of the 4 children of the doctor Thomas Henry McClintock and Sara Handy McClintock. She is independent with very an young age, a feature that McClintock described like its “capacity to be alone”. Towards the 3 years age until it begins the school, it lived in her aunt and her uncle in Massachusetts in order to decrease the financial expenses of her parents whereas his/her father began his medical practice. McClintock moved in 1908 with Brooklyn, New York. It was described like a solitary and independent child and a real tomboy. She was close to her father but had difficult relations with her mother.

McClintock supplemented its secondary education with the Erasmus Hall High School in Brooklyn. She discovered science with the secondary, and wanted to go to the Cornell University to continue her studies there. His/her mother resisted the idea that her daughters continue higher learning, fearing that they become non-mariables and that the family has financial problems. However his/her father intervened in his favor, and it entered in Cornell in 1919.

Education and research with Cornell

McClintock began its studies with the Cornell' S College off Agriculture in 1919. She studied the Botanique, and received her B.Sc in 1923. She discovered her interest for the genetics when she followed its first course in this field in 1921. This course was based on a similar course offered to the Université Harvard taught by C.B. Hutchison, a vegetable selector and a geneticist. Hutchinson was impressed by the shown interest of McClintock, and telephoned to him to invite it to take part in its graduated course of genetics in Cornell in 1922. McClintock accepted the invitation of Hutchinson for the reason which she wished to continue her studies in genetics: " Future Obviously, this telephone cal cast the die for my. I remained with genetics thereafter.".

Although it has been reported that women could not major in genetics At Cornell, and therefore her MY and PhD - earned in 1925 and 1927, respectively - were officially awarded in botany, recent research has revealed that women did earn graduate dismantle in Cornell' S Plant Breeding Department during the time that McClintock has student At Cornell. ,

During its studies graduated and its like teaching in botany, McClintock was a group studying a new field: cytogenetics of corn. This group was composed of selectors of plants and cytologists such as Charles R. Burnham, Marcus Rhoades, Harriet Creighton and George Wells Beadle (which became the prize winner of the Nobel of 1958 to have shown that the genes control it). Rollins Adams Emerson, the chief of the Plant Breeding Department supported these efforts, even if it were not itself cytologist.

Research in cytogenetics of McClintock related to the improvement in the manner of visualizing and of characterizing the Chromosome S of corn. This particular part of its work influenced a whole generation of students, and is included in the majority of the books of reference. It developed also a technique of coloring with the Carmin to visualize the chromosomes and showed for the first time the morphology of the 10 chromosomes of corn.

In 1930, McClintock was the first to describe interaction of the homologous chromosomes during the Méiose. In 1931, McClintock and its graduated coed, Harriet Creighton, proved the bond between Crossing-over chromosomes during the meiosis and the recombination of the genetic features. They observed how the recombination of the chromosomes and the resulting phenotype contribute to the heritage of a new feature. McClintock off published the first genetic card of corn in 1931, showing the order three constrained one maize chromosome 9. This information brought data necessary for the study of the crossing over which it published with Creighton.

University of Missouri - Columbia

During its years with Missouri, McClintock extended its research on the effect of x-rays on the cytogenetics of corn. It observed the break and the fusion of the Chromosome S at the corn cells irradiated. McClintock could as show as, at certain plants, a spontaneous break of the chromosome occurs in the cells of the Endosperme. During the Mitosis, it observed that the ends of the damaged chromosomes meet after the replication chromosome. At the stage of the Anaphase of the mitosis, the broken chromosomes form a bridge of Chromatide S, which breaks when the chromatides move towards the cellular poles. These damaged ends meet with the Interphase following mitosis, and the cycle is repeated, causing important changes, which it detected like the variegation in the endosperme. This cycle of breaking, fusion, bridging, also described like, was a key discovery in cytogenetics. Initially, that proved that the junction of the chromosomes was not a concerning event chance, and secondly, that showed a source of change to large scales. Still today, it is a field of interest for research on the Cancer.

Although its research progressed to Missouri, McClintock was not satisfied with its position at the University. She pointed out being excluded from the meetings facultaires, and was not briefing of the positions available in the others institutions. Initialement, the position of McClintock had been created especially for her by Stadler and was to depend on its presence. McClintock believed she would not profit Tenure At Missouri, although according to nap accounts she knew she would Be offered has off promotion by Missouri in the Spring 1942. Recent sources reveal that McClintock had probably decided to leave Missouri because it had lost confidence in its employers and the administration of the University.

Discovered elements controls

During the summer of 1944 with Cold Spring Harbor , McClintock began the systematic study from the mosaic of the owners of colors of the corn seeds and the instability of sound heritage. It identified two new loci genetic dominant interacting that it named Dissociator ( Ds ) and Activator ( ac ). It found that the Dissociator did not allow only dissociation but was also the cause of the break of the chromosome, and added a variety of effects on close genes when the Activator was also present. At the beginning of 1948, it made surprising it discovered that the Dissociator and Activator could transpose, or change position, on the chromosome. It observed the effects of the transposition of ac and Ds by the change of the owner of coloring of the corn grains through generations with the controlled crossing S, and described the relation between two loci using analysis microscopic complexes. She concluded from it that ac controlled the transposition of Ds chromosome 9, and that the movement of Ds was accompanied by the crack by the chromosome. When Ds moves, the Aleurone - color embarrassment is raised of its suppressor effect of Ds and is transformed into an active form, which initializes the synthesis of the pigment in the cells. The transposition of Ds is randomly made various cells, it is possible that it moves in some and others not, which causes the mosaic of colors. The size of the zone coloured on the seeds is determined by their developmental stage at the time of dissociation. McClintock also found that the transposition of Ds is determined by the number of copies of ac in the cell.

Between 1948 and 1950, it develops a theory carrying these variable components controlling genes by inhibition or modulation of their action. It used the words Dissociator and Activator like " controlling units" - later, like " controlling elements" - to distinguish them from genes. It put forth the assumption that the genic Régulation could explain how organizations multicellular S complexes made up of cells to the identical Génome could have cell S with the different functions. The discovery of McClintock defied the concept of a genome like a whole of static instructions last between the generations. In 1950, it published its work on Ac/Ds and its ideas on the genic regulation in an article entitled " The origin and behavior off mutable loci in maize" in the review Proceedings off the National Academy off Sciences . During the summer 1951, when it presented its work on the mutability of genes of corn to the annual symposium to Cold Spring Harbor, paper presented was rather entitled " Chromosome organization and genic expression".

Its work on the regulating elements and the genic regulation was conceptually difficult and was not immediately included/understood and was not accepted by its contemporaries; it described the reception of its research like " puzzlement, even hostility (perplexed, even hostile) ". In spite of that, McClintock continued to develop its ideas on the elements of control. It published an article in Genetics in 1953 when it presented all its statistical data and undertook in 1950 a lecture tour in the universities to speak as of its work. It continued its investigations and identified a new element which it named Suppressor-mutator ( Spm ), which, although similar to Ac/Ds showed a more complex behavior. Basing itself on the reactions of the other scientists to his work, McClintock felt that it was likely to alienate the current of thought dominating in science, and as from 1953, stopped publishing the results of its research on the elements of control.

Origins of corn

In 1957, McClintock accepted money of the the National Science Foundation, and the Fondation Rockefeller financed it so that it begins from research on corn in South America, a place rich in variety of Espèce S. It was interested in the evolution corn, and to go to South America enables him to work there. McClintock explored the characteristics chromosomal, morphological, and évolutionnaires of several Race S of corn. As from 1962, it supervised four scientists working on corn of South America to the Université of North Carolina, with Raleigh. Two of these member elects of Rockefeller, Almeiro Blumenschein and T. Angel Kato, continued their research on the races of but South American until the years 1970. In 1981, Blumenschein, Kato, and McClintock published Chromosome constitution off races off maize , which is regarded as the study reference on the corn and which contributed significantly to the fields of the botany of the evolution, the Ethnobotanique and the Paléobotanique.

Redécouverte of the elements of control of McClintock

McClintock took officially its retirement of its position of Carnegie in 1967, and it was made “Member distinguished from the service of Carnegie Institution of Washington”. This honor enabled him to continue its work with the graduated students and his/her colleagues of Cold Spring Laboratory as a scientific highly skilled . In reference to its decision taken 20 years earlier concerning more not publishing its results on the elements of control, she wrote in 1973:

Over the years I cuts found that it is difficult impossible yew not off to bring to consciousness another person the natural off his tacit assumptions when, by special nap experiments, I cuts been made aware off them. Obvious This became painfully to me in my attempts during the 1950s to convince geneticists that the action off constrained had to Be and was controlled. It is now equally painful to recognize the fixity off assumptions that many let us persons hold one the natural off controlling elements in maize and the manners off to their operation. One must await the right time for conceptual changes. Translation:

The importance of the contributions of McClintock was clarified in the years 1960, when the geneticists French François Jacob and Jacques Monod described the genetic regulation of the Opéron Lac, a concept which it had shown with Ac/Ds in 1951. Following the paper of Jacob and Monod of 1961 in the Newspaper off Molecular Biology , " Genetic regulatory mechanisms in the synthesis off proteins" , McClintock wrote an article for American Naturalist comparing the opéron lake and its work on the elements of control at corn. The contribution of McClintock to biology is not yet completely recognized like having contributed to discovered genetic regulation. Although Comfort argues that McClintock was not a victim of sexual Discrimination, it is quoted in several female studies ( women' S studies ), and certain recent work of biography on the women in sciences brings back her experiment to it. She plays there the part of a model for the girls in books of Children's literature such as those of Edith Hope Fine Barbara McClintock, Nobel Prize geneticist , of Deborah Heiligman Barbara McClintock: alone in her field and of Mary Kittredge Barbara McClintock . With recent biography for Young adults by Naomi Pasachoff, " Barbara McClintock, Genius off Genetics, provides has new perspective, based one the current literature.

McClintock was the high-speed motorboat of an emission of four stamps in 1989 in Sweden illustrating the work of geneticists having gained a Nobel Prize. Moreover, the May 4th 2005, the American Postal service published a series of postal stamps commemorating the American scientists, a whole of four stamps of 37 self-adhesive pennies in several configurations. The scientists represented were Barbara McClintock, John von Neumann, Josiah Willard Gibbs and Richard Feynman.

A building with the Université Cornell bears its name today.

Selected publications

McClintock, Barbara (1929) has cytological and genetical study off triploid maize. Genetics 14:180 - 222
Creighton, Harriet B., and McClintock, Barbara (1931) has off Correlation Cytological and Genetical Crossing-Over in Zea Mays. Proceedings off the National Academy off Sciences 17:492 - 497
McClintock, Barbara (1931) The order off the constrained C, HS, and Wx in Zea Mays with refer to has cytologically known not in the chromosome. Proceedings off the National Academy off Sciences 17:485 - 91
McClintock, Barbara (1941) The stability off broken ends off chromosomes in Zea Mays, Genetics 26:234 - 82
McClintock, Barbara (1945) Neurospora: preliminary observations off the chromosomes off Neurospora fouled. American Newspaper off Botany . 32:671 - 78
McClintock, Barbara (1950) The origin and behavior off mutable loci in maize. Proceedings off the National Academy off Sciences . 36:344 - 55
McClintock, Barbara (1953) Induction off instability At selected loci in maize. Genetics 38:579 - 99
McClintock, Barbara (1961) Somme parallels between embarrassment control systems in maize and in bacteria. American Naturalist 95:265 - 77
McClintock, Barbara., Kato, T.A. & Blumenschein, A. (1981) Chromosome constitution off races off maize. Its significance in the interpretation off relationships between races and varieties in the Americas. . Colegio de Postgraduados, Chapingo, Mexico City

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