Famous Scientist in Genetic Research – Barbara McClintock

barbara mcclintock (Image from Wikimedia Commons)Barbara McClintock is a famous scientist in genetic research for her pioneering works in the field of cytogenetics. She was awarded the Nobel Prize in Physiology and Medicine in 1983 for discovering “mobile genetic elements” in maize chromosomes. McClintock is among the few women scientists who excelled in scientific research despite of gender discriminations in their generation. McClintock is a woman of independence, excellence, hard work, and patience. This article provides a summary of the colorful and meaningful life of Barbara McClintock, famous scientist in genetic research.

Personal Life

Barbara McClintock was born on June 16, 1902 in Hartford, Connecticut. She was the 3rd of 4 children of physician Thomas Henry McClintock and Sara Handy McClintock. She was described as solitary and independent child. She lived with her uncle and aunt in Brooklyn, New York beginning at the age of three and until she started school. She was sent to her relatives to ease the financial burdens of her parents. She is closer to her father than to her mother, of whom she had difficult relationship.

When she finished high school, she wanted to continue her studies at Cornell University but her mother resisted the idea thinking that higher education would make her “unmarriageable” and their family also had financial problems. With the intervention of her father, she entered Cornell University in 1919.

McClintock never married and had children. She dedicated her life to genetic research.  She died on September 2, 1992 at the age of 90 in Huntington, New York, USA.

Education

  • Secondary education from Erasmus Hall High School, Brooklyn, New York
  • B.S. Cornell University, Ithaca, New York, 1923
  • M.A. Cornell University, Ithaca, New York, 1925
  • Ph.D. Cornell University, Ithaca, New York, 1927

Positions Held

  • 1927-1931: Instructor in botany, Cornell University
  • 1931-1933: Fellow, National Research Council
  • 1933-1934: Fellow, Guggenheim Foundation
  • 1934-1936: Research Associate, Cornell University
  • 1936-1941: Assistant Professor, University of Missouri, Columbia, Missouri
  • 1942-1967: Staff Member, Carnegie Institution of Washington, Cold Spring Harbor, New York
  • 1967-1992: Distinguished Service Member, Carnegie Institution of Washington, Cold Spring Harbor, New York
  • 1954: Visiting Professor, California Institute of Technology
  • 1965-1974: Andrew D. White Professor-at-Large, Cornell University, 1965-1974

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Important Contributions to Genetic Research

In Cornell University, McClintock research has focused on the cytogenetics of maize. She developed ways to characterize and visualize the ten chromosomes of maize, which include a staining technique using carmine dye to study chromosomal morphology. She was the first scientist to show the morphology of maize chromosomes and also the first one to link a specific chromosome to a group of traits inherited together in the plant.

In 1931, McClintock became the first scientist to describe the cross-shaped interaction of homologous chromosomes during meiosis. She and her graduate student, Harriet Creighton, were able to prove the connection between chromosomal crossover during meiosis and recombination of genetic traits. They learned that genetic recombination through chromosome crossover results in the inheritance of new traits or phenotypes.

McClintock was again the first scientist to publish a genetic map for maize in 1931. The genetic map shows the order of three genes in chromosome 9. In 1938, she described the function and structure of the centromere.

When she moved at the University of Missouri, she observed that x-ray increases the rate of mutation by causing damage to the chromosomes. Using a microscope, McClintock observed that the ends of a single chromosome fused together to form a ring after radiation damage. She hypothesized that there is a structure at the tip of every chromosome that ensure stability. Later on, other scientists have found that the structure earlier described by McClintock was actually the telomere which functions in maintaining chromosomal stability.

When she worked as researcher at Cold Spring Harbor Laboratory in 1944, she produced a karyotype of Neurospora crassa, an important model organism for genetics. The fungus was first used to study one gene-one enzyme relationship.

While at Cold Spring, McClintock also began studying the mosaic color patterns of maize seed and the unstable inheritance of this trait. She identified two new dominant and interacting genetic loci, the Dissociator (Ds) and Activator (Ac). She observed that Ds can cause chromosome breakage and can affect neighboring genes in the presence of Ac. She was surprised when she found out that the Ds and Ac could change position within the chromosome by transposition.

Barbara McClintock Corn Genetics (Image from Wikimedia Commons)According to McClintock, the genetic transposition in maize chromosome changes the patterns of corn kernel coloration over generations of controlled crosses. She called the Ds and Ac loci as “controlling elements” because they work together to control or regulate the expression of other genes in the chromosome. She added that the “controlling elements” would explain why multicellular organisms made up of cells with identical genome have cells with different functions.

After McClintock published her work in 1953, she received a lot of criticisms from her contemporaries. The concept of “controlling elements” was hardly understood by other scientists. One big reason why McClintock idea had not received great support from other scientists is because it contradicts the mainstream knowledge that the genome is a “static set of instructions passed between generations.”

McClintock stopped publishing her works on transposable or mobile genes because she felt that she is alienating the scientific mainstream. Her discovery was rediscovered in 1961 by two scientists who studied the genetic regulation of lac operon in bacteria. McClintock’s discovery on the “controlling elements” (Ac & Dc) is similar to the concept of lac operon.

McClintock’s early discovery on genetic transposition have been validated by succeeding researches. Later on, the mobile genetic elements (Ac and Ds) were named “transposons”. Many people began to realize the importance of McClintock’s discovery in genetics as well as in other biological disciplines such as evolution and developmental biology. She then received various recognitions and awards from different institutions and universities around the world.

Awards and Recognitions

The most notable award received by Dr. McClintock was the Nobel Prize in Physiology or Medicine in 1983 for her discovery of “mobile genetic elements” (also known as “jumping genes”) in maize chromosomes. She received the award 30 years after she published her findings on the transposable genes in maize. Other awards and recognitions to Dr. McClintock are the following:

  • 12 Honorary Doctorates in Science from 1947 to 1983
  • 1 Honorary Doctorate in Humane Letters from Georgetown University 1981
  • 1947: Achievement Award, Association of University Women
  • 1957: Merit Award, Botanical Society of America
  • 1970: National Medal of Science
  • 1980: Salute from the Genetics Society of America
  • 1981: Thomas Hunt Morgan Medal. Genetics Society of America
  • 1981: Honorary Member, The Society of Developmental Biology
  • 1981: MacArthur Prize Fellow Laureate
  • Others

McClintock was also depicted in a commemorative postage stamp released by the United States Postal Service on 2005. Buildings in Cornell University and Cold Spring Harbor Laboratory bear her name.

Other Famous Scientists in Genetic Research


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References