Barbara McClintock

Barbara McClintock (Hartford, United States, June 16, 1902 – Huntington, United States, September 3, 1992) was an American scientist specializing in cytogenetics who was awarded the Nobel Prize in Medicine. or Physiology in 1983.

McClintock received his doctorate in botany in 1927 from Cornell University, where he later led the maize cytogenetics group, his field of interest throughout his career. At the end of the 1920s, he studied the changes that occur in the chromosomes during maize reproduction, revealing through microscopy methods developed in his laboratory processes as fundamental as the genetic recombination that occurs during meiosis. As the initiator of genetic mapping in maize, she described the first linkage map of this genome and highlighted the role of telomeres and centromeres. Due to the high level of her scientific work, she was awarded several times, becoming part of the National Academy of Sciences of the United States in 1944.

In the 1940s and 1950s, McClintock discovered the process of rearranging elements of the genome and used it to explain how genes determine certain physical characteristics. He developed hypotheses about the regulation of gene expression and the transmission of traits from parental to progeny maize plants. These investigations were viewed with skepticism by his colleagues, which caused him to stop publishing his data in 1953. After this he devoted himself to the study of the cytogenetics and ethnobotany of South American races of maize. During the 1960s and 1970s, other scientists published the mechanisms of regulation of gene expression that she had described and postulated more than twenty years earlier.

As an award for her discoveries in the field of genetic transposition, she was awarded the Nobel Prize alone. She was the first woman to win the Nobel Prize in Medicine and the only one to have received such recognition alone.

Biography

McClintock Family 1907

Barbara McClintock was born in Hartford, Connecticut. Although she was initially registered as Eleanor, she amended her registration at four months of age by making the name change by which she was known, Barbara.She was the third child of Thomas Henry McClintock, a physician, and Sara Handy. McClintock. She displayed great independence from an early age, which she would describe as her "ability to be on her own" from her. From the time she was three years old until she began attending college, McClintock lived with her aunt and uncle in Brooklyn, New York, in order to help her family financially while her father established her practice. She has been described as an independent and lonely girl. She was closer to her father than to her mother, and as an adult she noted that both had been very supportive of her, but that her relationship with her mother had been cold.

He completed his secondary education at Erasmus Hall High School in Brooklyn. Since he already showed an interest in science, he decided to continue his studies at Cornell University. His mother, however, was opposed to her daughters receiving a higher education, as she believed that this hurt their chances of marriage. In addition, the family continued with financial problems. However, McClintock enjoyed tuition exemption at the Cornell College of Agriculture, and after finishing high school, he combined a job in an employment office with self-taught training derived from the use of the public library. at the intervention of her father, she began to attend Cornell in 1919. There her success would not only be academic but also social, being elected president of a student association in her first year.

Training and research at Cornell

Stone Hall, Roberts Hall and East Roberts Hall were the first buildings of the New York State School of Agriculture

McClintock began studying at the Cornell College of Agriculture in 1919. He studied botany, earning a Bachelor of Science (BSc) degree in 1923. His interest in genetics was sparked in 1921 during the first course of that subject; this, directed by plant breeder and geneticist C. B. Hutchison, was similar to that offered at Harvard University. Due to the exceptional interest shown by McClintock, Hutchinson invited her to participate in the graduate course in Genetics in 1922. In the words of McClintock, that invitation marked a before and after after which she would never move away from Genetics. Although it has been said that women did not obtain degrees in this discipline at Cornell (in fact, she obtained her MA or graduate degree and PhD or doctorate in Botany in the years 1925 and 1927, respectively), other female students of McClintock's age graduated in Plant Breeding at that time.

Both in her undergraduate studies and as a postgraduate botany professor, McClintock worked in the emerging field of maize cytogenetics. His group was a mix of plant breeders and cytologists, and included Charles R. Burnham, Marcus Rhoades, George Wells Beadle (1958 Nobel laureate for work on genes controlling metabolism), and Harriet Creighton. Rollins Adams Emerson, the head of the department, supported his work, although he was not a cytologist.

As the main objective of his work, McClintock developed techniques to visualize and characterize maize chromosomes. This work influenced an entire generation of students, and was included in most textbooks. He produced a technique based on carmine staining for the aforementioned visualization of chromosomes by light microscopy, showing for the first time the morphology of the ten chromosomes of maize. By studying this morphology, he was able to relate characters that were inherited jointly with chromosome segments (linkage analysis). Marcus Rhoades noted that McClintock's 1929 article in the scientific journal Genetics, dealing with triploidy of maize chromosomes, contained 10 of the 17 major scientific advances made at Cornell during the years 1929-1935.

In 1930 he was the first person to describe the crossing over that occurs between homologous chromosomes during meiosis. Together with her pre-doctoral student, Harriet Creighton, she proved in 1931 that there is a relationship between this meiotic chromosomal crossing over and the recombination of heritable characters. They observed that chromosome recombination and the resulting phenotype led to the inheritance of a new trait. Prior to this discovery, it was postulated that genetic recombination could occur during meiosis. In 1931 McClintock published the order of three genes on chromosome 9 of maize by genetic mapping resulting from an understanding of the mechanism of linkage and crossing over. This study led to Creighton's publication on this topic. In 1933, he conducted a cytogenetic study of the centromere, showing its organization and function.

Due to his extraordinary scientific output and the support of his colleagues, McClintock has won several awards and postdoctoral fellowships from the United States National Research Council (the engineering equivalent of the United States National Academy of Sciences). This led to further studies at Cornell, the University of Missouri, and the California Institute of Technology, where he worked with E. G. Anderson. During the summers of 1931 and 1932, he worked in Missouri with the geneticist Lewis Stadler., which brought him the use of X-rays as a mutagenic agent. Using mutagenized maize lines in this way, he identified ring chromosomes, which are circular DNA structures generated by the fusion of the ends of a single irradiated chromosome. Analyzing this result, McClintock hypothesized that there must be a structure at the ends of the chromosomes. to stabilize them. Furthermore, he showed that these circular chromosomes caused a variegated pattern in maize leaves, due to deletion of the chromosome in successive generations. During this period, he further demonstrated the existence of the nucleolar organizer in a region of maize chromosome 6, which is essential for nucleolus assembly.

McClintock received a Guggenheim Foundation fellowship that paid for six months of apprenticeship in Germany during 1933 and 1934. His plan was to work with Curt Stern, a researcher who demonstrated interbreeding in Drosophila weeks after it she and Creighton did the same in corn; however, Stern immigrated to the United States just then. Therefore, the acceptor laboratory for her turned out to be Richard B. Goldschmidt. Due to political tension in Germany at the time, she shortened the length of her stay and returned to Cornell, where she remained until 1936, when she obtained an assistant professorship in the Department of Botany at the University of Missouri-Columbia.

University of Missouri

During her time as a researcher in Missouri, McClintock continued the line of X-ray mutagenesis. She observed that chromosomes break and fuse under these conditions, but also that they do so spontaneously in endosperm cells. During mitosis, she described how the ends of broken chromatids came together after DNA replication. Specifically, during anaphase the broken chromosomes formed a chromatid bridge, which in turn disappeared when the chromatids moved towards the cell poles. These breaks disappeared (i.e., giving rise to unions) during interphase of the next mitosis, repeating the cycle and causing massive mutations, leading to the appearance of variegated endosperm. This cycle of breaking, fusing, and bridging chromosomes was considered a crucial discovery: firstly, because it showed that the union of chromosomes was not a random process; and secondly, because she detected a mechanism for the production of mutations on a large scale. For this reason, this mechanism is the subject of intense study in cancer research.

Although her investigation was progressing in Missouri, McClintock was dissatisfied with her position. For example, she was excluded from faculty meetings, and was not notified of vacancies at other institutions.In 1936, an engagement advertisement for a woman of the same name appeared in newspapers. Mistaking this woman for her, the head of her department threatened to fire her if she married (McClintock was then vice president of the American Genetic Society). In 1940 she wrote to Charles Burnham that "I have decided that I should look for another job. There is nothing for me here. I'm an associate professor making $3,000 and I'm sure that's my limit in this place." Her position was initially created especially for her, and because Stadler was her instigator, she relied of his presence. McClintock thought he would never get the starting job at Missouri, although he might have received an offer in the spring of 1942. Evidence has recently come to light that McClintock left Missouri because he lost confidence in his coordinator and in the administration of the University. In 1941 he received an invitation from the director of the Department of Genetics at the Cold Spring Harbor Laboratory to spend the summer there. She accepted the invitation as a way to look for a job in a place other than Missouri. She also accepted a visiting professorship at Columbia University, where her Cornell colleague Marcus Rhoades was a professor. He offered to share her research line in Cold Spring Harbor on Long Island. In December 1941, Milislav Demerec, her new director, offered her a research position at the Cold Spring Harbor Laboratory belonging to the Department of Genetics of the Carnegie Institution of Washington, which she accepted.

Cold Spring Harbor

After working part-time for a year, McClintock accepted a full-time research position at the Cold Spring Harbor laboratory. In it she continued her work on the "break-fusion-bridge" cycle, she being extraordinarily productive in scientific publications. Due to this productivity, in 1944 she was recognized as an academic in the National Academy of Sciences of the United States, thus being the third woman to be elected. A year later she would be named president of the Genetics Society of America, a position previously held by men. At George Beadle's suggestion, in 1944 she performed a cytogenetic analysis on the fungus Neurospora crassa ; in this mushroom Beadle had demonstrated the gene-enzyme relationship for the first time. Said study was carried out at Stanford University, and in it McClintock determined the karyotype of the fungus as well as its life cycle. Since then, N. crassa is a model organism in genetic studies.

Discovery of regulatory elements

McClintock spent the summer of 1944 in the Cold Spring Harbor laboratory elucidating the mechanism underlying the phenomenon of genetic mosaic, which generates color patterns in corn seeds, and its genetic inheritance. Thus, he described two loci which he termed Dissociator ( Ds ) and Activator ( Ac ). Ds was not only related to chromosome breakage, but affected the activity of nearby genes when Ac was also present. In 1948, he discovered that both loci were transposable elements that could therefore change their position on the chromosome.

He studied the effects of rearranging Ac and Ds by analyzing color patterns in maize nuclei over generations, intervening in crosses, and described the relationship between the two loci by microscopy analysis. His conclusion was that Ac controlled the transposition of Ds of chromosome 9, and that this movement was the cause of the breakage of the chromosome. When Ds moves, the gene that determines the color of the aleurone is expressed since it loses the repressor effect of Ds, which leads to the appearance of color. Said transposition is random, which means that it affects some cells and not others; this causes the appearance of a mosaic in the infructescence. McClintock also determined that the transposition of Ds is determined by the number of copies of Ac.

The relationship Ac/Ds in control of the elements and color mosaic of the corn. The seed in 10 is colourless, where Ac is not present and Ds inhibits the synthesis of colored pigments called anthocyanins. From 11 to 13, the seeds have a copy of Ac. Ds may partially inhibit the production of pigments, which causes the appearance of a pattern in mosaic. In the core of panel 14 there are two elements Ac and in 15, three.

Between 1948 and 1959, he developed a hypothesis that explained how transposable elements regulate the action of genes by inhibiting or modulating them. Thus, he defined Ds and Ac as control units , or regulatory elements , to clearly separate them. of genes. Thus, he hypothesized that gene regulation may explain how multicellular organisms can diversify the characteristics of each cell, even when their genome is identical. This novel approach changed the concept of the genome, which until then was interpreted as a set of static instructions that passed through the generations. In 1950 he published the work on Ac/Ds and gene regulation in the journal Proceedings of the National Academy of Sciences under the title “The origin and behavior of mutable loci in maize» ("The origin and behavior of mutable loci in maize"). The following year, at the Cold Spring Harbor Laboratory's annual symposium, he gave a talk on the subject entitled "Chromosome organization and genic expression" ("Organization of chromosomes and gene expression").

His work on gene regulation and control elements was conceptually complex and novel, so his contemporaries were somewhat suspicious of his discoveries; she herself described that response as "bewildered and even hostile". Regardless, McClintock continued her line of inquiry. Starting in 1950, he made a multitude of papers on his results, which he published in 1953 in the journal Genetics. Later, he identified a new regulatory element called the "Suppressor-mutator" (Spm), which, while similar to Ac/Ds, was more complex in operation. However, the reaction of the scientific community and McClintock's perception of alienating herself from the scientific mainstream of her contemporaries caused her to decide to stop publishing her results on this topic.

Origins of corn

Barbara McClintock with one of his results.

In 1957, McClintock obtained funding from the National Science Foundation and the Rockefeller Foundation to study maize in South America, a region that has a rich diversity of species and therefore would allow him to study their biological evolution. For this purpose he used several races, of which he described evolutionary, chromosomal and morphological characteristics. Since 1962, he has supervised the work of four scientists working on South American varieties at North Carolina State University in Raleigh. Two of these fellows, Almiro Blumenschein and T. Angel Kato, continued the line of research in South America until the 1970s. In 1981 (after twenty years of work), Blumcschein, Kato and McClintock published "Chromosome constitution of races of maize» ("Chromosomal composition of maize races"), which is considered a milestone in the studies of ethnobotany, paleobotany and evolutionary botany.

Rediscovering the regulatory elements

McClintock officially retired from her position at the Carnegie Institution in 1967, being named a distinguished fellow there. This distinction allowed him to continue working as a scientist emeritus at the Cold Spring Harbor Laboratory with his colleagues and graduate students; in fact, she remained affiliated with the laboratory until her death.Regarding her decision not to proceed with publication of her findings on regulatory elements, she wrote in 1973 that:

Over the years I have discovered that it is difficult, if not impossible, to make another person aware of his tacit assumptions if, through my experiences, I have been. This became painfully evident in the 1950s when I tried to convince my colleagues that the action of genes had to be and was controlled. Today it is equally painful to recognize the immobility of the assumptions that other people maintained regarding the regulatory elements in corn and its mode of action. One must wait for the right time for a conceptual change.

Barbara McClintock, 1973

The importance of McClintock's work was only fully appreciated when in the 1960s the French geneticists François Jacob and Jacques Monod reached similar conclusions working with the lac operon. After their publication in 1961 from the article “Genetic regulatory mechanisms in the synthesis of proteins” in the Journal of Molecular Biology, McClintock wrote an article in American Naturalist comparing the functioning of the lac operon to the Ac/Ds system of maize. In fact, genetics textbooks do not yet acknowledge his contributions to gene regulation.

McClintock was widely recognized for her discovery of transposition when this process was described by others in bacteria and yeast in the late 1960s and early 1970s. At this time, molecular biology tools made it possible to elucidate the molecular basis of the process. In the 1970s, she cloned Ac and Ds and were shown to be class II transposons. Ac is a complete transposon, encoding in its sequence a functional transposase, allowing movement of the element through the genome. Ds, on the other hand, encodes a mutated version of transposase, which is non-functional, and therefore requires the presence of Ac in order to jump into the genome; this fits McClintock's functional description. Spm is also a transposon. Subsequent studies showed that these sequences do not move if the cells are not undergoing stress, such as rupture by radiation or others; for this reason, their activation could provide an evolutionary source of variability. McClintock understood their role as evolutionary agents before other scientists suspected it. Today, the Ac/Ds system is used as a plant mutagenesis tool to characterize genes of unknown function, even in species other than maize.

Recognition and distinctions

McClintock on December 8, 1983, giving a speech included in the Nobel conferences.

McClintock was awarded the 1971 National Medal of Science by Richard Nixon. Cold Spring Harbor also named a building after her in 1973. In 1981, she was the first recipient of the John D. and Catherine T. MacArthur Foundation Fellowship, informally known as the "Genius" Fellowship; recipient of the Albert Lasker Award for Basic Medical Research, the Wolf Prize in Medicine, and the Thomas Hunt Morgan Medal of the Genetics Society of America. In 1982, Columbia University awarded her the Louisa Gross Horwitz Prize for her work on the "evolution of genetic information and the regulation of its expression." In 1983, she received the Nobel Prize in Medicine or Physiology for her work on transposable elements, thirty years after she did it.

Academically, he received fourteen honoris causa doctorates in Science, as well as one in Humanities. In 1986, she was inducted into the National Women's Hall of Fame. During the last years of her life, and especially after the publication of her biography (written in 1983 by Evelyn Fox Keller), McClintock had a major impact on public life. Thus, she was a regular speaker in the Cold Spring Harbor community, where her audience was often made up of young scientists. In 1987, an anthology of his 43 most relevant works was published called "The discovery and characterization of transposable elements: the collected papers of Barbara McClintock".: compilation of articles by Barbara McClintock").

The relevance of McClintock's academic work can be approximated by evaluating the number of publications by other authors who have used one of his articles as a reference; as of 2010, these citations numbered 1,450, with an average of 131 per article. McClintock, however, was always sensitive to the scientific landscape around her; perceiving that his studies on the regulation of gene expression were too innovative for the scientific mainstream of the time, he decided to postpone the publication of his results. However, this lack of publication in professional journals was compatible with the dissemination of his results. to the environment of non-skeptical colleagues. His work philosophy is reflected in the opinion he expressed in 1983 (the year the Nobel was awarded):

Over the years I have really enjoyed not being forced to defend my interpretations. I could just work with the greatest pleasure. I never felt the need, nor the desire, to defend my views. If anything turned out to be incorrect, I simply forgot to share that perspective. It didn't matter.

Barbara McClintock, 1983.

McClintock died of natural causes on September 2, 1992 at Huntington Hospital, near the Cold Spring Harbor Laboratory, at the age of ninety; he left no descendants.

Last years

McClintock spent her final years, after winning the Nobel Prize, as the lead researcher at the Cold Spring Harbor Laboratory on Long Island, New York. In addition, she continued to give lectures on genetics in different places in the United States. She died of natural causes in Huntington, New York, on September 2, 1992, aged 90. She never married or had children.

Legacy

A microscope of McClintock and corn scrubs, as shown in the National Museum of Natural History of the Smithsonian Institution.

After her death, McClintock aroused the interest of science historian Nathaniel C. Comfort, who wrote a biography called "The tangled field: Barbara McClintock's search for the patterns of genetic control" ("The Tangled Field: Barbara McClintock's Search for Patterns of Genetic Control"). In this biography, Comfort presents a view that differs from Keller's biography. Where Keller noted that McClintock had long been neglected for being a woman, Keller argues that she was recognized by her peers even in the early years of her scientific career. Despite this demystification of possible discrimination, numerous subsequent works have employed her figure in the diffusion of the figure of the scientific woman; for example, in children's books such as "Barbara McClintock: Alone in Her Field" by Deborah Heiligman, "Barbara McClintock, Nobel Prize Geneticist" by Edith Hope Fine or "Barbara McClintock" by Mary Kittredege. A youth-oriented biography was published in 2006 offering an up-to-date analysis.

On May 4, 2005, the United States Postal Service printed a series of commemorative postage stamps inside "American scientists"; in them appeared McClintock, John von Neumann, Josiah Willard Gibbs, and Richard Feynman. In 1989, Switzerland did the same with the eight Nobel Prize-winning geneticists. A small building at Cornell University, as well as a laboratory at the Cold Spring Harbor Laboratory bear his name. Also like this a street of the science park in Berlin.

Key Publications

Barbara McClintock in 1978, together with George P. Redei during the Stadler Genetics symposium at the University of Missouri-Columbia.

• McClintock, Barbara (1929) «A cytological and genetical study of triploid maize». Genetics 14:180–222.

In it, McClintock describes an individual triploid from a diploid culture. To do this, it describes the meotic events of the microsporocites of the specimen, performing a cariotype and observing the trend of chromosomal grouping during the events leading to the distribution of copies in gametes. It performs a reciprocal cross with diploid corn (the conventional one). It notes from the agronomic perspective that the triploid variant has a smaller size and vigor.

• Creighton, Harriet B., and McClintock, Barbara (1931) «A Correlation of Cytological and Genetical Crossing-Over in Zea mays». Proceedings of the National Academy of Sciences 17:492–497.

The work describes through cytogenetic techniques the intercruzation events between heteromorphic chromosomes. In addition, it monitors the transmission of variants to progenie, establishing the frequencies of appearance of the different combinations of recombined chromosomes and without recombining. It shows that there is an exchange of genes between chromosomes that is transmitable to the offspring.

• McClintock, Barbara (1931) «The order of the genes C, Sh, and Wx in Zea Mays with reference to a cytologically known point in the chromosome». Proceedings of the National Academy of Sciences 17:485–91.

This article uses specimens of corn with easily classifiable phenotypes (e.g., with a certain color of the alleurone in the grains or possessors of a slightly different composition starch) in order to perform a genetic analysis of the order of their genes; that is, it implies an approximation of genetic cartography based on the ligation analysis. Therefore, it makes an association between the physical situation of genes in the genome and the characteristics of individuals.

• McClintock, Barbara (1941) «The stability of broken ends of chromosomes in Zea Mays». Genetics 26:234–82.

McClintock describes the "rupture-fusion-bridge" phenomenon that occurs in some chromosomes when the corn specimen is under stress. Based on the cytogenetic characterization of chromosomes in different phases of cell division, it describes the process and its consequence, the emergence of massive mutations. Outside the purely molecular perspective, it relates this source of variability (from the mutation of the genetic acquis) to the appearance of a variegated endosperma.

• McClintock, Barbara (1945) «Neurospora: preliminary observations of the chromosomes of Neurospora crassa». American Journal of Botany. 32:671-78.

During the ten weeks of stay in Standford laboratories, McClintock studied the nuclear characteristics of some strains, both wild and mutant, of filamentous ascomicete. Neurospora crassa. In this article, it describes the characteristics of meiosis and mitosis in the fungus, highlighting the novel aspects of the organisms previously studied.

• McClintock, Barbara (1950) «The origin and behavior of mutable loci in maize». Proceedings of the National Academy of Sciences. 36:344–55.

In 1950 it had already been described by phenotypic characterization that in the fruit fly, Drosophila melanogaster, there was a source of variability that was described as "dependent of position" in the chromosomal structure. Since McClintock also observed this phenomenon in corn, he hypothesized in this article that the generation of new variants was due to the existence of "control units" or "regulatory elements"; according to this hypothesis, these were DNA fragments other than genes that were able to modulate the expression of genes.

• McClintock, Barbara (1953) «Induction of instability at selected loci in maize». Genetics 38:579–99.

In this article McClintock continues with his work of genetic cartography and ligation analysis, explaining the nature of chromosomal alterations leading to the appearance of variegated phenotypes according to his hypothesis of regulatory elements. In order to demonstrate to his skeptical colleagues that his model was correct, he describes the methodology necessary to detect Ac/Ds action in chromosomes 3 and 5 of corn.

• McClintock, Barbara (1961) «Some parallels between gene control systems in maize and in bacteria». American Naturalist 95:265–77.

The publication in 1959 of another gene regulation system in bacteria, the opera lac by Francois Jacob and Jacques Monod, constituted a validation of the McClintock hypothesis. This article compares both systems, similar and existing in phylogeneticly far-off organisms.

• McClintock, Barbara., Kato, T. A. & Blumenschein, A. (1981) «Chromosome constitution of races of maize. Its significance in the interpretation of relationships between races and varieties in the Americas». College of Postgraduates, Chapingo, Mexico.

The sampling and study of American varieties of corn, which the McClintock team performed for more than two decades, was published as a book in which the scientific approach was markedly multidisciplinary. Since corn is also a model organism a crop of great relevance in food, its team raised the diversity of corn from the cytological but also ethnobotanical, paleobotanical and evolutionary aspect.

Brief timeline

Brief McClintock timeline:

• 1902: Eleanor McClintock was born in Hartford, Connecticut; at four months, he changed his name for Barbara.
• 1908: His family moved to Brooklyn, New York.
• 1919: He graduates at the Erasmus Hall High School in Brooklyn, where he studied secondary education. Decide to study at Cornell.
• 1919-25: Obtains the titles of BSc (1923) and MSc (1925) of Botánico in his master soul, Cornell University.
• 1927: Obtains PhD (doctorate) in Botanics at the same University.
• 1927-31: Charge of researcher and instructor in maize genetics, Cornell University.
• 1931: It publishes, with H. Creighton as co-author, an article on interscruces in corn.
• 1931: Publishes genetic transmission studies.
• 1931: National Research Council Fellowship; researches at Cornell, the University of Missouri in Columbia and the California Institute of Technology.
• 1933-34: Fellowship of the Guggenheim Foundation; research at the Kaiser Wilhelm Institute in Berlin, and the Botanic Institute in Freiburg, Germany.
• 1934-36: Place of research at Cornell University.
• 1936-40: Place of Associate Professor of Genetics, University of Missouri in Columbia.
• 1941-67: Researcher's Square in Genetics, Carnegie Institution at Long Island Cold Spring Harbor Laboratory, New York.
• 1944: Member of the National Academy of Sciences of the United States.
• 1945: President of the Society of Genetics of America.
• 1951: Controverted talk at the Cold Spring Harbor Symposium on Maize Regulatory Elements.
• 1957-66: Beginning of the study of corn breeds in South America; sampling trips.
• 1967: Carnegie Institution Award for its distinguished service; this membership remains until the year of its death.
• 1971: National Medal of Science granted by Richard Nixon.
• 1981: Fellowship of the MacArthur Foundation: first scholarship and with vitality privileges.
• 1981: Albert and Mary Lasker Award.
• 1983: Nobel Prize in Medicine or Physiology.
• 1992: He died in Huntington, New York.

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