Barbara McClintock
Born	June 16, 1902(1902-06-16) Hartford, Connecticut, USA
Died	September 2, 1992 (aged 90) Huntington, New York, USA
Nationality	United States
Fields	Cytogenetics
Institutions	University of Missouri Cold Spring Harbor Laboratory
Alma mater	Cornell University
Notable awards	Nobel Prize in Physiology or Medicine (1983)

Barbara McClintock (June 16, 1902 – September 2, 1992) the 1983 Nobel Laureate in Physiology or Medicine, was an American scientist and one of the world's most distinguished cytogeneticists. Events 1487 - Battle of Stoke Field, the last dying breath of the Wars of the Roses. Year 1902 ( MCMII) was a Common year starting on Wednesday (link will display calendar of the Gregorian calendar (or a Common year starting The United States of America —commonly referred to as the Events 44 BC - Pharaoh Cleopatra VII of Egypt declares her son co-ruler as Ptolemy XV Caesarion. Year 1992 ( MCMXCII) was a Leap year starting on Wednesday (link will display full 1992 Gregorian calendar) The Town of Huntington is a town located on the North Shore of Long Island, in northwestern Suffolk County, New York. The United States of America —commonly referred to as the The United States of America —commonly referred to as the Cytogenetics is a branch of Genetics that is concerned with the study of chromosomes and cell division The University of Missouri (also known as the University of Missouri–Columbia, Mizzou, or MU) is a public land-grant and research The Cold Spring Harbor Laboratory (CSHL is a private non-profit institution with research programs focusing on Cancer, Neurobiology, Plant genetics, Alma mater is Latin for "nourishing mother" It was used in Ancient Rome as a title for the mother Goddess, and in Medieval The Nobel Prize in Physiology or Medicine (Nobelpriset i fysiologi eller medicin is awarded once a year by the Swedish Karolinska Institute. Events 1487 - Battle of Stoke Field, the last dying breath of the Wars of the Roses. Year 1902 ( MCMII) was a Common year starting on Wednesday (link will display calendar of the Gregorian calendar (or a Common year starting Events 44 BC - Pharaoh Cleopatra VII of Egypt declares her son co-ruler as Ptolemy XV Caesarion. Year 1992 ( MCMXCII) was a Leap year starting on Wednesday (link will display full 1992 Gregorian calendar) The Nobel Prize in Physiology or Medicine (Nobelpriset i fysiologi eller medicin is awarded once a year by the Swedish Karolinska Institute. The United States of America —commonly referred to as the Cytogenetics is a branch of Genetics that is concerned with the study of chromosomes and cell division McClintock received her PhD in botany from Cornell University in 1927, where she was a leader in the development of maize cytogenetics. "PhD" redirects here for other uses see PhD (disambiguation. Botany, plant science(s, phytology, or plant biology is a branch of Biology and is the scientific study of plant Life Maize (ˈmeɪz ( Zea mays L. ssp mays) known as corn in some countries is a cereal grain domesticated in Mesoamerica The field remained the focus of her research for the rest of her career. From the late 1920s, McClintock studied chromosomes and how they change during reproduction in maize. The 1920s is sometimes referred to as the " Jazz Age " or the " Roaring Twenties " when speaking about the United States and Canada A chromosome is an organized structure of DNA and Protein that is found in cells. Her work was groundbreaking: she developed the technique for visualizing maize chromosomes and used microscopic analysis to demonstrate many fundamental genetic ideas, including genetic recombination by crossing-over during meiosis—a mechanism by which chromosomes exchange information. Genetic recombination is the process by which a strand of genetic material (usually DNA; but can also be RNA) is broken and then joined to a different DNA molecule In Biology or life science meiosis (pronounced my-oh-sis is a process of reductional division in which the number of chromosomes per cell is cut in half She produced the first genetic map for maize, linking regions of the chromosome with physical traits, and she demonstrated the role of the telomere and centromere, regions of the chromosome that are important in the conservation of genetic information. Genetic linkage occurs when particular genetic loci or Alleles for genes are inherited jointly A telomere is a region of repetitive DNA at the end of Chromosomes which protects the end of the chromosome from destruction A centromere is a region of DNA typically found near the middle of a Chromosome where two Sister chromatids come in contact She was recognized amongst the best in the field, awarded prestigious fellowships and elected a member of the National Academy of Sciences in 1944.

During the 1940s and 1950s, McClintock discovered transposition and used it to show how genes are responsible for turning physical characteristics on or off. The 1940s decade ran from 1940 to 1949 Events and trends The 1940s was a period between the radical 1930s and the conservative 1950s which also leads the period to be The 1950s Decade refers to the years of 1950 to 1959 inclusive Transposons are sequences of DNA that can move around to different positions within the Genome of a single cell, a process called transposition History See also History of genetics The existence of genes was first suggested by Gregor Mendel (1822-1884 who in the 1860s studied inheritance She developed theories to explain the repression or expression of genetic information from one generation of maize plants to the next. Encountering skepticism of her research and its implications, she stopped publishing her data in 1953. Later, she made an extensive study of the cytogenetics and ethnobotany of maize races from South America. Ethnobotany ( from " ethnology " - study of culture and " Botany " - study of plants) is the scientific study of the relationships In biology a race is any inbreeding group including taxonomic subgroups such as Subspecies, taxonomically subordinate to a Species and superordinate to a subrace McClintock's research became well understood in the 1960s and 1970s, as researchers demonstrated the mechanisms of genetic change and genetic regulation that she had demonstrated in her maize research in the 1940s and 1950s. Gene modulation redirects here For information on therapeutic regulation of gene expression see Therapeutic gene modulation. Awards and recognition of her contributions to the field followed, including the Nobel Prize, awarded to her in 1983 for the discovery of genetic transposition; to date, she has been the first and only woman to receive an unshared Nobel Prize in that category. Transposons are sequences of DNA that can move around to different positions within the Genome of a single cell, a process called transposition

Early life

Barbara McClintock was born in Hartford, Connecticut, the third of four children of physician Thomas Henry McClintock and Sara Handy McClintock. She was independent from a very young age, a trait McClintock described as her "capacity to be alone. " From about the age of three until the time she started school, McClintock lived with an aunt and uncle in Massachusetts in order to reduce the financial burden on her parents while her father established his medical practice. The McClintocks moved to semi-rural Brooklyn, New York in 1908. Brooklyn (named after the Dutch town Breukelen) is one of the five boroughs of New York City. She was described as a solitary and independent child, and a tomboy. She was close to her father, but had a difficult relationship with her mother. ^[1]

McClintock completed her secondary education in Erasmus Hall High School in Brooklyn. Erasmus Hall Campus High School is a three-year Public high school in the New York City borough of Brooklyn, operated as part of the New Brooklyn (named after the Dutch town Breukelen) is one of the five boroughs of New York City. ^[2] She discovered science at high school, and wanted to attend Cornell University to continue her studies. Her mother resisted the idea of higher education for her daughters, believing that it would make them unmarriageable, and the family also had financial problems. Barbara was almost prevented from starting college, but her father intervened, and she entered Cornell in 1919.

Education and research at Cornell

McClintock began her studies at Cornell's College of Agriculture in 1919. She studied botany, receiving a BSc in 1923. Botany, plant science(s, phytology, or plant biology is a branch of Biology and is the scientific study of plant Life Her interest in genetics had been sparked when she took her first course in that field in 1921. The course was based on a similar one offered at Harvard University, and was taught by C. B. Hutchison, a plant breeder and geneticist. Claude Burton Hutchison ( April 9, 1885 – August 25, 1980) was a botanist agricultural economist educator and Mayor of the City of ^[3] Hutchinson was impressed by McClintock's interest, and telephoned to invite her to participate in the graduate genetics course at Cornell in 1922. McClintock pointed to Hutchinson's invitation as the reason she continued in genetics: "Obviously, this telephone call cast the die for my future. I remained with genetics thereafter. "^[4] Although it has been reported that women could not major in genetics at Cornell, and therefore her MA and PhD — earned in 1925 and 1927, respectively — were officially awarded in botany, recent research has revealed that women did earn graduate degrees in Cornell's Plant Breeding Department during the time that McClintock was a student at Cornell. ^[5]

During her graduate studies and her postgraduate appointment as a botany instructor, McClintock was instrumental in assembling a group that studied the new field of cytogenetics in maize. Cytogenetics is a branch of Genetics that is concerned with the study of chromosomes and cell division Maize (ˈmeɪz ( Zea mays L. ssp mays) known as corn in some countries is a cereal grain domesticated in Mesoamerica This group brought together plant breeders and cytologists, and included, Charles R. Burnham, Marcus Rhoades, and George Beadle (who became a Nobel laureate in 1958 for showing that genes control metabolism), and Harriet Creighton. Marcus Morton Rhoades ( July 24, 1903 in Graham Missouri - December 30, 1991) was an American cytogeneticist George Wells Beadle ( October 22, 1903 &ndash June 9, 1989) was an American Scientist in the field of Genetics ^[6] Rollins Adams Emerson, head of the Plant Breeding Department supported these efforts, although he was not a cytologist himself. ^[7] McClintock's cytogenetic research focused on developing ways to visualize and characterize maize chromosomes. This particular part of her work influenced a generation of students, as it was included in most textbooks. She also developed a technique using carmine staining to visualize maize chromosomes, and showed for the first time the morphology of the 10 maize chromosomes. ^[8] By studying the morphology of the chromosomes, McClintock was able to link to a specific chromosome groups of traits that were inherited together. Genetic linkage occurs when particular genetic loci or Alleles for genes are inherited jointly Marcus Rhoades noted that McClintock's 1929 Genetics paper on the characterization of triploid maize chromosomes triggered scientific interest in maize cytogenetics, and attributed to his female colleague 10 of the 17 significant advances in the field that were made by Cornell scientists between 1929 and 1935. Genetics (not to be confused with the Indian publication Journal of Genetics) is a monthly Scientific journal publishing investigations bearing Polyploidy occurs in cells and Organisms when there are more than two homologous sets of Chromosomes. ^[9]

In 1930, McClintock was the first person to describe the cross-shaped interaction of homologous chromosomes during meiosis. During 1931, McClintock and a graduate student, Harriet Creighton, proved the link between chromosomal crossover during meiosis and the recombination of genetic traits. Harriet Baldwin Creighton ( 27 June 1909 &ndash January 9 2004) was an American Botanist, Geneticist and educator In Biology or life science meiosis (pronounced my-oh-sis is a process of reductional division in which the number of chromosomes per cell is cut in half ^[10] They observed how the recombination of chromosomes and the resulting phenotype formed the inheritance of a new trait. ^[11] Until this point, it had only been hypothesized that genetic recombination could occur during meiosis, although it had been shown genetically. Genetic recombination is the process by which a strand of genetic material (usually DNA; but can also be RNA) is broken and then joined to a different DNA molecule McClintock published the first genetic map for maize in 1931, showing the order of three genes on maize chromosome 9. ^[12] This information provided necessary data for the crossing over study she published with Creighton. ^[13] In 1938, she produced a cytogenetic analysis of the centromere, describing the organization and function of the centromere. A centromere is a region of DNA typically found near the middle of a Chromosome where two Sister chromatids come in contact

McClintock's breakthrough publications, and support from her colleagues, led to her being awarded several postdoctoral fellowships from the National Research Council. The National Research Council (NRC of the USA is the working arm of the United States National Academy of Sciences and the United States National Academy of This funding allowed her to continue to study genetics at Cornell, the University of Missouri, and the California Institute of Technology, where she worked with E. The University of Missouri (also known as the University of Missouri–Columbia, Mizzou, or MU) is a public land-grant and research The California Institute of Technology (commonly referred to as Caltech) is a private, Coeducational research university located in Pasadena G. Anderson. ^[14] During the summers of 1931 and 1932, she worked with geneticist Lewis Stadler at Missouri, who introduced her to the use of X-rays as a mutagen. Lewis John Stadler ( July 6, 1896 - May 12, 1954) was an American geneticist X-radiation (composed of X-rays) is a form of Electromagnetic radiation. In Biology, a mutagen ( Latin, literally origin of change) is a physical or chemical agent that changes the genetic information (usually DNA) (Exposure to X-rays 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 maize, she identified ring chromosomes, which form when the ends of a single chromosome fuse together after radiation damage. A ring chromosome is a chromosome whose arms have fused together to form a ring From this evidence, McClintock hypothesized that there must be a structure on the chromosome tip that would normally ensure stability. She showed that the loss of ring-chromosomes at meiosis caused variegation in maize foliage in generations subsequent to irradiation resulting from chromosomal deletion. Variegation is the appearance of differently coloured zones in the leaves, and sometimes the stems, of Plants This may be due to a number of causes During this period, she demonstrated the presence of what she called the nucleolar organizers on a region on maize chromosome 6, which is required for the assembly of the nucleolus during DNA replication. Nucleolus organizer region (NOR is a chromosomal region around which the Nucleolus forms The nucleolus (also called nucleole) is a structure found within the nucleus in which Ribosomal RNA is transcribed.

McClintock received a fellowship from the Guggenheim Foundation that made possible six months of training in Germany during 1933 and 1934. She had planned to work with Curt Stern, who had demonstrated crossing-over in Drosophila just weeks after McClintock and Creighton had done so; however, in the meantime, Stern emigrated to the United States. Curt Stern ( August 30 1902 - October 23 1981) was a German - American Geneticist. Drosophila is a Genus of small flies, belonging to the family Drosophilidae, whose members are often called "fruit flies" Instead, she worked in Germany with geneticist Richard B. Goldschmidt. Richard Benedict Goldschmidt ( April 12, 1878 – April 24, 1958) was a German -born American Geneticist. She left Germany early, amid mounting political tension in Europe, and returned to Cornell, remaining there until 1936, when she accepted an Assistant Professorship offered to her by Lewis Stadler in the Department of Botany at the University of Missouri–Columbia. ^[15]

University of Missouri–Columbia

During her time at Missouri, McClintock expanded her research on the effect of X-rays on maize cytogenetics. McClintock observed the breakage and fusion of chromosomes in irradiated maize cells. She was also able to show that, in some plants, spontaneous chromosome breakage occurred in the cells of the endosperm. Over the course of mitosis, she observed that the ends of broken chromatids were rejoined after the chromosome replication. Mitosis is the process in which a Eukaryotic cell separates the Chromosomes in its Cell nucleus, into two identical sets in two daughter nuclei DNA replication is the process of copying a double-stranded DNA molecule to form two double-stranded molecules In the anaphase of mitosis, the broken chromosomes formed a chromatid bridge, which was broken when the chromatids moved towards the cell poles. Anaphase, from the Ancient Greek ἀνά (up and φάσις (stage is the stage of Mitosis when Chromosomes The broken ends were rejoined in the interphase of the next mitosis, and the cycle was repeated, causing massive mutation, which she could detect as variegation in the endosperm. Interphase is the phase of the Cell cycle in which the cell spends the majority of its time and performs the majority of its purposes including preparation for Cell ^[16] This cycle of breakage, fusion, and bridge, also described as the breakage–rejoining–bridge cycle, was a key cytogenetic discovery for several reasons. First it showed that the rejoining of chromosomes was not a random event, and secondly it demonstrated a source of large-scale mutation. For this reason, it remains an area of interest in cancer research today. Cancer (medical term Malignant Neoplasm) is a class of Diseases in which a group of cells display uncontrolled

Although her research was progressing at Missouri, McClintock was not satisfied with her position at the University. She recalled being excluded from faculty meetings, and was not made aware of positions available at other institutions. ^[1] In 1940 she wrote to Charles Burnham, "I have decided that I must look for another job. As far as I can make out, there is nothing more for me here. I am an assistant professor at $3,000 and I feel sure that that is the limit for me. "^[17] Initially, McClintock's position had been especially created for her by Stadler and may have depended on his presence. ^[18] McClintock believed she would not gain tenure at Missouri, although according to some accounts she knew she would be offered a promotion by Missouri in the Spring of 1942. Tenure commonly refers to life tenure in a job and specifically to a senior Academic 's Contractual right not to have their position terminated ^[19] Recent evidence reveals that McClintock more likely decided to leave Missouri because she had lost trust in her employer and in the University administration. ^[18] In early 1941 she was invited by the Director of the Department of Genetics at Cold Spring Harbor to spend her summer there. She took a leave of absence from Missouri in hopes of finding a position elsewhere. She also accepted a visiting Professorship at Columbia University, where her former Cornell colleague Marcus Rhoades was a professor. Columbia University is a private University in the United States and a member of the Ivy League. He offered to share his research field at Cold Spring Harbor on Long Island. In December 1941 she was offered a research position by Milislav Demerec, the newly appointed acting director and she joined the staff of the Carnegie Institution of Washington's Department of Genetics Cold Spring Harbor Laboratory. Milislav Demerec ( January 11, 1895 &ndash April 12, 1966) was a Croatian &mdash American Geneticist, and the The Carnegie Institution for Science (also called the Carnegie Institution of Washington (CIW) is a organization in the United States established to support Scientific The Cold Spring Harbor Laboratory (CSHL is a private non-profit institution with research programs focusing on Cancer, Neurobiology, Plant genetics,

Cold Spring Harbor

After her year-long temporary appointment, McClintock accepted a full-time research position at Cold Spring Harbor. The Cold Spring Harbor Laboratory (CSHL is a private non-profit institution with research programs focusing on Cancer, Neurobiology, Plant genetics, Here, she was highly productive and continued her work with the breakage-fusion-bridge cycle, using it to substitute for X-rays as a tool for mapping new genes. In 1944, in recognition of her prominence in the field of genetics during this period, McClintock was elected to the National Academy of Sciences — only the third woman to be so elected. The National Academy of Sciences (NAS is a corporation in the United States whose members serve Pro bono as "advisers to the nation on science In 1945, she became the first woman president of the Genetics Society of America. The Genetics Society of America is a non-exclusive association of Genetics researchers and educators and the publisher of the peer-reviewed journal Genetics In 1944 she undertook a cytogenetic analysis of Neurospora crassa at the suggestion of George Beadle, who had used the fungus to demonstrate the one gene–one enzyme relationship. Neurospora crassa is a type of red bread mold of the phylum Ascomycota. He invited her to Stanford to undertake the study. Leland Stanford Junior University, commonly known as Stanford University or simply Stanford, is a private Research university located in She successfully described the number of chromosomes, or karyotype, of N. A karyotype is the characteristic Chromosome complement of a Eukaryote Species. crassa and described the entire life cycle of the species. N. crassa has since become a model species for classical genetic analysis. A model organism is a Species that is extensively studied to understand particular biological Phenomena, with the expectation that discoveries made ^[20]

Discovery of controlling elements

The relationship of Ac/Ds in the control of the elements and mosaic color of maize. The seed in 10 is colorless, there is no Ac element present and Ds inhibits the synthesis of colored pigments called anthocyanins. Not to be confused with Anthocyanidin, their sugar free counterparts In 11 to 13, one copy of Ac is present. Ds can move and some anthocyanin is produced, creating a mosaic pattern. In the kernel in panel 14 there are two Ac elements and in 15 there are three.

In the summer of 1944 at Cold Harbor Spring McClintock began systematic studies on the mechanisms of the mosaic color patterns of maize seed and the unstable inheritance of this mosaicism. In Medicine ( Genetics) a mosaic or mosaicism denotes the presence of two populations of cells with different Genotypes in one She identified two new dominant and interacting genetic loci that she named Dissociator (Ds) and Activator (Ac). She found that the Dissociator did not just dissociate or cause the chromosome to break, it also had a variety of effects on neighboring genes when the Activator was also present. In early 1948, she made the surprising discovery that both Dissociator and Activator could transpose, or change position, on the chromosome.

She observed the effects of the transposition of Ac and Ds by the changing patterns of coloration in maize kernels over generations of controlled crosses, and described the relationship between the two loci through intricate microscopic analysis. In the fields of Genetics and Evolutionary computation, a locus (plural loci) is a fixed position on a Chromosome such as the position of a She concluded that Ac controls the transposition of the Ds from chromosome 9, and that the movement of Ds is accompanied by the breakage of the chromosome. When Ds moves, the aleurone-color gene is released from the suppressing effect of the Ds and transformed into the active form, which initiates the pigment synthesis in cells. Aleurone (from Greek aleuron, flour is a Protein found in protein granules of maturing Seeds and Tubers The term is also used for The transposition of Ds in different cells is random, it may move in some but not others, which causes color mosaicism. The size of the colored spot on the seed is determined by stage of the seed development during dissociation. McClintock also found that the transposition of Ds and the is determined by the number of Ac copies in the cell.

Between 1948 and 1950, she developed a theory by which these mobile elements regulated the genes by inhibiting or modulating their action. She referred to Dissociator and Activator as "controlling units"—later, as "controlling elements"—to distinguish them from genes. She hypothesized that gene regulation could explain how complex multicellular organisms made of cells with identical genomes have cells of different function. Gene modulation redirects here For information on therapeutic regulation of gene expression see Therapeutic gene modulation. In classical genetics the genome of a Diploid Organism including Eukarya refers to a full set of chromosomes or genes in a Gamete, thereby McClintock's discovery challenged the concept of the genome as a static set of instructions passed between generations. In 1950, she reported her work on Ac/Ds and her ideas about gene regulation in a paper entitled "The origin and behavior of mutable loci in maize" published in the journal Proceedings of the National Academy of Sciences. The Proceedings of the National Academy of Sciences of the United States of America, usually referred to as PNAS, is the official journal of the United In summer 1951, when she reported on her work on gene mutability in maize at the annual symposium at Cold Spring Harbor, the paper she presented was called "Chromosome organization and genic expression". ^[21]

Her work on controlling elements and gene regulation was conceptually difficult and was not immediately understood or accepted by her contemporaries; she described the reception of her research as "puzzlement, even hostility". ^[22] Nevertheless, McClintock continued to develop her ideas on controlling elements. She published a paper in Genetics in 1953 where she presented all her statistical data and undertook lecture tours to universities throughout the 1950s to speak about her work. Genetics (not to be confused with the Indian publication Journal of Genetics) is a monthly Scientific journal publishing investigations bearing ^[23] She continued to investigate the problem and identified a new element that she called Suppressor-mutator (Spm), which, although similar to Ac/Ds displays more complex behavior. Based on the reactions of other scientists to her work, McClintock felt she risked alienating the scientific mainstream, and from 1953 stopped publishing accounts of her research on controlling elements. ^[24]

The origins of maize

McClintock's microscope and ears of corn on exhibition at the National Museum of Natural History. The National Museum of Natural History is a Natural history Museum administered by the Smithsonian Institution, located on the National

In 1957, McClintock received funding from the National Science Foundation, and the Rockefeller Foundation sponsored her to start research on maize in South America, an area that is rich in varieties of this species. The National Science Foundation (NSF is a United States Government agency that supports fundamental Research and Education in all the non-medical The Rockefeller Foundation (RF is a prominent Philanthropic organization and Private foundation based at 420 Fifth Avenue New York City. South America is a Continent of the Americas, situated entirely in the Western Hemisphere and mostly in the Southern Hemisphere, with a She was interested in studying the evolution of maize, and being in South America would allow her to work on a larger scale. eVolution is the third Album by eLDee, it was due to be released in 2008 McClintock explored the chromosomal, morphological, and evolutionary characteristics of various races of maize. In biology a race is any inbreeding group including taxonomic subgroups such as Subspecies, taxonomically subordinate to a Species and superordinate to a subrace From 1962, she supervised four scientists working on South American maize at the North Carolina State University in Raleigh. Two of these Rockefeller fellows, Almeiro Blumenschein and T. Angel Kato, continued their research on South American races of maize well into the 1970s. In 1981, Blumenschein, Kato, and McClintock published Chromosome constitution of races of maize, which is considered a landmark study of maize that has contributed significantly to the fields of evolutionary botany, ethnobotany, and paleobotany. Ethnobotany ( from " ethnology " - study of culture and " Botany " - study of plants) is the scientific study of the relationships Paleobotany, also spelled as palaeobotany (from the Greek words paleon = old and " Botany " study of plants is the branch of

Rediscovery of McClintock's controlling elements

McClintock officially retired from her position at the Carnegie Institution in 1967, and was made a Distinguished Service Member of the Carnegie Institution of Washington. This honor allowed her to continue working with graduate students and colleagues in the Cold Spring Laboratory as scientist emerita. In reference to her decision 20 years earlier no longer to publish detailed accounts of her work on controlling elements, she wrote in 1973:

Over the years I have found that it is difficult if not impossible to bring to consciousness of another person the nature of his tacit assumptions when, by some special experiences, I have been made aware of them. This became painfully evident to me in my attempts during the 1950s to convince geneticists that the action of genes had to be and was controlled. It is now equally painful to recognize the fixity of assumptions that many persons hold on the nature of controlling elements in maize and the manners of their operation. One must await the right time for conceptual change. ^[25]

The importance of McClintock's contributions only came to light in the 1960s, when the work of French geneticists Francois Jacob and Jacques Monod described the genetic regulation of the lac operon, a concept she had demonstrated with Ac/Ds in 1951. François Jacob (born 17 June 1920 in Nancy France) is a French Biologist who together with Jacques Monod, originated See also Jacques-Louis Monod, French-born composer and cousin of Jacques Monod The lac operon is an Operon required for the transport and Metabolism of Lactose in Escherichia coli and some other Following Jacob and Monod's paper 1961 Journal of Molecular Biology paper "Genetic regulatory mechanisms in the synthesis of proteins", McClintock wrote an article for American Naturalist comparing the lac operon and her work on controlling elements in maize. American Naturalist is a monthly Scientific journal, founded in 1867 and associated with the American Society of Naturalists. ^[26] McClintock's contribution to biology is still not widely acknowledged as amounting to the discovery of genetic regulation. ^[24]

McClintock was widely credited for discovering transposition following the discovery of the process in bacteria and yeast in the late 1960s and early 1970s. During this period, molecular biology had developed significant new technology, and scientists were able to show the molecular basis for transposition. In the 1970s, Ac and Ds were cloned by other scientists and were shown to be Class II transposons. Cloning in Biology is the process of producing populations of genetically-identical individuals that occurs in nature when organisms such as Bacteria, Insects Transposons are sequences of DNA that can move around to different positions within the Genome of a single cell, a process called transposition Ac is a complete transposon that can produce a functional transposase, which is required for the element to move within the genome. Transposase is an Enzyme that binds to single-stranded DNA and can incorporate it into genomic DNA Ds has a mutation in its transposase gene, which means that it cannot move without another source of transposase. Thus, as McClintock observed, Ds cannot move in the absence of Ac. Spm has also been characterized as a transposon. Subsequent research has shown that transposons typically do not move unless the cell is placed under stress, such as by irradiation or the breakage, fusion, and bridge cycle, and thus their activation during stress can serve as a source of genetic variation for evolution. McClintock understood the role of transposons in evolution and genome change well before other researchers grasped the concept. Nowadays, Ac/Ds is used as a tool in plant biology to generate mutant plants used for the characterization of gene function.

Honors and recognition

McClintock was awarded the National Medal of Science by Richard Nixon in 1971. The National Medal of Science is an honor bestowed by the President of the United States to individuals in Science and Engineering who have made important Cold Spring Harbor named a building in her honor in 1973. In 1981 she became the first recipient of the MacArthur Foundation Grant, and was awarded the Albert Lasker Award for Basic Medical Research, the Wolf Prize in Medicine and the Thomas Hunt Morgan Medal by the Genetics Society of America. The John D and Catherine T MacArthur Foundation is a major private grant -making Private foundation based in Chicago that has awarded more than US$4 billion The Albert Lasker Award for Basic Medical Research is one of the prizes awarded by the Lasker Foundation for the understanding diagnosis prevention treatment The Thomas Hunt Morgan Medal is a medal awarded for lifetime contributions to the field of Genetics. In 1982 she was awarded the Louisa Gross Horwitz Prize from Columbia University for her research in the "evolution of genetic information and the control of its expression. Louisa Gross Horwitz Prize for Biology or Biochemistry is an annual prize awarded by Columbia University to a researcher or group of researchers that have made an outstanding Columbia University is a private University in the United States and a member of the Ivy League. " Most notably, she received the Nobel Prize for Physiology or Medicine in 1983, credited by the Nobel Foundation for discovering "mobile genetic elements", over thirty years after she initially described the phenomenon of controlling elements. The Nobel Prize in Physiology or Medicine (Nobelpriset i fysiologi eller medicin is awarded once a year by the Swedish Karolinska Institute. The Nobel Foundation (Nobelstiftelsen is a private institution founded on 29 June 1900 to manage the finances and administration of the Nobel Prizes.

She was awarded 14 Honorary Doctor of Science degrees and an Honorary Doctor of Humane Letters. In 1986 she was inducted into the National Women's Hall of Fame. The National Women's Hall of Fame was created in 1969 by a group of people in Seneca Falls, New York, the location of the 1848 Women's Rights Convention During her final years, McClintock led a more public life, especially after Evelyn Fox Keller's 1983 book A feeling for the organism brought McClintock's story to the public. Evelyn Fox Keller (born 1936 is an American Physicist, Author, and feminist and is currently a Professor of History and Philosophy of Science She remained a regular presence in the Cold Spring Harbor community, and gave talks on mobile genetic elements and the history of genetics research for the benefit of junior scientists. An anthology of her 43 publications The discovery and characterization of transposable elements: the collected papers of Barbara McClintock was published in 1987. McClintock died in Huntington, New York, on September 2, 1992 at the age of 90; she never married or had children. The Town of Huntington is a town located on the North Shore of Long Island, in northwestern Suffolk County, New York. Events 44 BC - Pharaoh Cleopatra VII of Egypt declares her son co-ruler as Ptolemy XV Caesarion. Year 1992 ( MCMXCII) was a Leap year starting on Wednesday (link will display full 1992 Gregorian calendar)

Legacy

Since her death, McClintock has been the subject of the biographical work by science historian Nathaniel C. Comfort, in The tangled field : Barbara McClintock's search for the patterns of genetic control. Nathaniel C Comfort is an American historian specialising in the history of biology Comfort's biography contests some claims about McClintock, described as the "McClintock Myth", which he claims was perpetuated by the earlier biography by Keller. Keller's thesis was that McClintock was long ignored because she was a woman working in the sciences, whereas Comfort asserts that McClintock was well regarded by her professional peers, even in the early years of her career. ^[27] Although Comfort argues that McClintock was not a victim of sex discrimination, she has been widely written about in the context of women's studies, and most recent biographical works on women in science feature accounts of her experience. She is held up as a role model for girls in such works of children's literature as Edith Hope Fine's Barbara McClintock, Nobel Prize geneticist, Deborah Heiligman's Barbara McClintock: alone in her field and Mary Kittredge's Barbara McClintock. A recent biography for young adults by Naomi Pasachoff, Barbara McClintock, Genius of Genetics, provides a new perspective, based on the current literature. ^[28]

On May 4, 2005 the United States Postal Service issued the American Scientists commemorative postage stamp series, a set of four 37-cent self-adhesive stamps in several configurations. Events 1256 - The Augustinian monastic order is constituted at the Lecceto Monastery when Pope Alexander IV Year 2005 ( MMV) was a Common year starting on Saturday (link displays full calendar of the Gregorian calendar. A postage stamp is an adhesive paper evidence of pre-paying a fee for postal services The scientists depicted were Barbara McClintock, John von Neumann, Josiah Willard Gibbs, and Richard Feynman. Josiah Willard Gibbs ( February 11, 1839 &ndash April 28, 1903) was an American theoretical Physicist, Chemist Richard Phillips Feynman (ˈfaɪnmən May 11 1918 – February 15 1988 was an American Physicist known for the Path integral formulation of quantum McClintock was also featured in a 1989 four-stamp issue from Sweden which illustrated the work of eight Nobel Prize-winning geneticists. "Sverige" redirects here For other uses see Sweden (disambiguation and Sverige (disambiguation. A small building at Cornell University and a laboratory building at Cold Spring Habor Laboratory bear her name to this day.

Key publications

• McClintock, Barbara (1929) A cytological and genetical study of triploid maize. Genetics 14:180–222
• 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
• 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
• McClintock, Barbara (1941) The stability of broken ends of chromosomes in Zea Mays, Genetics 26:234–82
• McClintock, Barbara (1945) Neurospora: preliminary observations of the chromosomes of Neurospora crassa. American Journal of Botany. 32:671–78
• McClintock, Barbara (1950) The origin and behavior of mutable loci in maize. Proceedings of the National Academy of Sciences. 36:344–55
• McClintock, Barbara (1953) Induction of instability at selected loci in maize. Genetics 38:579–99
• McClintock, Barbara (1961) Some parallels between gene control systems in maize and in bacteria. American Naturalist 95:265–77
• 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. . Colegio de Postgraduados, Chapingo, Mexico

References

Further reading

External links

• Cold Spring Harbor Laboratory Archives, Barbara McClintock:A Brief Biographical Sketch
• Enhancer and Gene Trap Transposon Mutagenesis in Arabidopsis, comprehensive article on the use of Ac/Ds and other transposons for plant mutagenesis
• The Official Site of Louisa Gross Horwitz Prize