Gregor Mendel

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Gregor Mendel
Gregor Mendel oval.jpg
Born Johann Mendel
(1822-07-20)20 July 1822
Heinzendorf bei Odrau, Austrian Empire (now Hynčice, Czech Republic)
Died 6 January 1884(1884-01-06) (aged 61)
Brno (Brünn), Austria-Hungary (now Czech Republic)
Nationality Empire of Austria-Hungary
Fields Genetics
Institutions St Thomas's Abbey
Alma mater University of Olomouc
University of Vienna
Known for Creating the science of genetics

Gregor Johann Mendel (20 July 1822[1] – 6 January 1884) was a German-speaking Silesian[2][3] scientist and Augustinian friar who gained posthumous fame as the founder of the modern science of genetics. Though farmers had known for centuries that crossbreeding of animals and plants could favor certain desirable traits, Mendel's pea plant experiments conducted between 1856 and 1863 established many of the rules of heredity, now referred to as the laws of Mendelian inheritance.

Mendel worked with seven characteristics of pea plants: plant height, pod shape and color, seed shape and color, and flower position and color. With seed color, he showed that when a yellow pea and a green pea were bred together their offspring plant was always yellow. However, in the next generation of plants, the green peas reappeared at a ratio of 1:3. To explain this phenomenon, Mendel coined the terms “recessive” and “dominant” in reference to certain traits. (In the preceding example, green peas are recessive and yellow peas are dominant.) He published his work in 1866, demonstrating the actions of invisible “factors”—now called genes—in providing for visible traits in predictable ways.

The profound significance of Mendel's work was not recognized until the turn of the 20th century (more than three decades later) with the independent rediscovery of these laws.[4] Erich von Tschermak, Hugo de Vries, Carl Correns, and William Jasper Spillman independently verified several of Mendel's experimental findings, ushering in the modern age of genetics.

Biography

Johann Mendel was born into an ethnic German family in Heinzendorf bei Odrau, Austrian Silesia, Austrian Empire (now Hynčice, Czech Republic). (He was given the name Gregor when he joined the Augustinian friars.[5]) He was the son of Anton and Rosine (Schwirtlich) Mendel, and had one older sister, Veronika, and one younger, Theresia. They lived and worked on a farm which had been owned by the Mendel family for at least 130 years.[6] During his childhood, Mendel worked as a gardener and studied beekeeping. Later, as a young man, he attended gymnasium in Opava. He had to take four months off during his gymnasium studies due to illness. From 1840 to 1843, he studied practical and theoretical philosophy and physics at the University of Olomouc Faculty of Philosophy, taking another year off because of illness. He also struggled financially to pay for his studies and Theresia gave him her dowry. Later he helped support her three sons, two of whom became doctors. He became a friar because it enabled him to obtain an education without having to pay for it himself.[7]

When Mendel entered the Faculty of Philosophy, the Department of Natural History and Agriculture was headed by Johann Karl Nestler who conducted extensive research of hereditary traits of plants and animals, especially sheep. Upon recommendation of his physics teacher Friedrich Franz,[8] Mendel entered the Augustinian St Thomas's Abbey and began his training as a priest. Born Johann Mendel, he took the name Gregor upon entering religious life. Mendel worked as a substitute high school teacher. In 1850 he failed the oral part, the last of three parts, of his exams to become a certified high school teacher. In 1851 he was sent to the University of Vienna to study under the sponsorship of Abbot C. F. Napp so that he could get more formal education.[9] At Vienna, his professor of physics was Christian Doppler.[10] Mendel returned to his abbey in 1853 as a teacher, principally of physics. In 1856 he took the exam to become a certified teacher and again failed the oral part.[9]In 1867 he replaced Napp as abbot of the monastery.[11]

Mendel began his studies on heredity using mice. He was at St. Thomas's Abbey but his bishop did not like one of his friar studying animal sex, so Mendel switched to plants.[12] Mendel also bred bees in a bee house that was built for him, using bee hives that he designed.[13] He also studied astronomy and meteorology,[11] founding the 'Austrian Meteorological Society' in 1865.[10] The majority of his published works were related to meteorology.[10]

Experiments on plant hybridization

Dominant and recessive phenotypes. (1) Parental generation. (2) F1 generation. (3) F2 generation.

Gregor Mendel, who is known as the "father of modern genetics", was inspired by both his professors at the University of Olomouc (Friedrich Franz & Johann Karl Nestler) and his colleagues at the monastery (e.g., Franz Diebl) to study variation in plants, and he conducted his study in the monastery's 2 hectares (4.9 acres) experimental garden,[14] which was originally planted by Napp in 1830.[11] Unlike Nestler, who studied hereditary traits in sheep, Mendel focused on plants. After initial experiments with pea plants, Mendel settled on studying seven traits that seemed to inherit independently of other traits: seed shape, flower color, seed coat tint, pod shape, unripe pod color, flower location, and plant height. He first focused on seed shape, which was either angular or round.[15] Between 1856 and 1863 Mendel cultivated and tested some 29,000 pea plants (i.e., Pisum sativum). This study showed that one in four pea plants had purebred recessive alleles, two out of four were hybrid and one out of four were purebred dominant. His experiments led him to make two generalizations, the Law of Segregation and the Law of Independent Assortment, which later came to be known as Mendel's Laws of Inheritance.

Mendel presented his paper, Versuche über Pflanzenhybriden (Experiments on Plant Hybridization), at two meetings of the Natural History Society of Brno in Moravia on 8 February and 8 March 1865.[16] It was received favorably and generated reports in several local newspapers.[17] When Mendel's paper was published in 1866 in Verhandlungen des naturforschenden Vereins Brünn,[18] it was seen as essentially about hybridization rather than inheritance and had little impact and was cited about three times over the next thirty-five years. Notably, Charles Darwin was unaware of Mendel's paper, according to Jacob Bronowski's The Ascent of Man. His paper was criticized at the time, but is now considered a seminal work.

Life after the pea experiments

After completing his work with peas, Mendel turned to experimenting with honeybees to extend his work to animals. He produced a hybrid strain (so vicious they were destroyed) but failed to generate a clear picture of their heredity because of the difficulties in controlling mating behaviours of queen bees.[dubious ] He also described novel plant species, and these are denoted with the botanical author abbreviation "Mendel".

After he was elevated as abbot in 1868, his scientific work largely ended, as Mendel became consumed with his increased administrative responsibilities, especially a dispute with the civil government over their attempt to impose special taxes on religious institutions.[19] Mendel died on 6 January 1884, at the age of 61, in Brno, Moravia, Austria-Hungary (now Czech Republic), from chronic nephritis. Czech composer Leoš Janáček played the organ at his funeral. After his death, the succeeding abbot burned all papers in Mendel's collection, to mark an end to the disputes over taxation.[20]

Rediscovery of Mendel's work

Mendel's work was rejected at first in the scientific community, and was not widely accepted until after he died. During his own lifetime, most biologists held the idea that all characteristics were passed to the next generation through blending inheritance, in which the traits from each parent are averaged together. Instances of this phenomenon are now explained by the action of multiple genes with quantitative effects. Charles Darwin tried unsuccessfully to explain inheritance through a theory of pangenesis. It was not until the early 20th century that the importance of Mendel's ideas was realized.

By 1900, research aimed at finding a successful theory of discontinuous inheritance rather than blending inheritance led to independent duplication of his work by Hugo de Vries and Carl Correns, and the rediscovery of Mendel's writings and laws. Both acknowledged Mendel's priority, and it is thought probable that de Vries did not understand the results he had found until after reading Mendel.[4] Though Erich von Tschermak was originally also credited with rediscovery, this is no longer accepted because he did not understand Mendel's laws.[21] Though de Vries later lost interest in Mendelism, other biologists started to establish genetics as a science.[4] All three of these researchers, each from a different country, published their work rediscovering Mendel's work within a two-month span in the Spring of 1900.[22]

Mendel's results were quickly replicated, and genetic linkage quickly worked out. Biologists flocked to the theory; even though it was not yet applicable to many phenomena, it sought to give a genotypic understanding of heredity which they felt was lacking in previous studies of heredity which focused on phenotypic approaches. Most prominent of these previous approaches was the biometric school of Karl Pearson and W.F.R. Weldon, which was based heavily on statistical studies of phenotype variation. The strongest opposition to this school came from William Bateson, who perhaps did the most in the early days of publicising the benefits of Mendel's theory (the word "genetics", and much of the discipline's other terminology, originated with Bateson). This debate between the biometricians and the Mendelians was extremely vigorous in the first two decades of the twentieth century, with the biometricians claiming statistical and mathematical rigor, whereas the Mendelians claimed a better understanding of biology.

In the end, the two approaches were combined, especially by work conducted by R. A. Fisher as early as 1918. The combination, in the 1930s and 1940s, of Mendelian genetics with Darwin's theory of natural selection resulted in the modern synthesis of evolutionary biology.

Hybridizing experiments

In 1854, Mendel started his hybridizing experiments. He focused on the origin of plant variability. He tested the purities of selected varieties of Pisum and then began experiments with artificial fertilization. Mendel's experimental data illustrates that he must have been tested 28,000 Pisum plants during the years 1856–63.

Controversy

Mendel's experimental results have later been the object of considerable dispute.[20] Fisher analyzed the results of the F2 (second filial) ratio and found them to be implausibly close to the exact ratio of 3 to 1.[23] Reproduction of his experiments has demonstrated the validity of his hypothesis, but the results have continued to be a mystery for many, though it is often cited as an example of confirmation bias. This might arise if he detected an approximate 3 to 1 ratio early in his experiments with a small sample size, and continued collecting more data until the results conformed more nearly to an exact ratio. It is sometimes suggested that he may have censored his results, and that his seven traits each occur on a separate chromosome pair, an extremely unlikely occurrence if they were chosen at random. In fact, the genes Mendel studied occurred in only four linkage groups, and only one gene pair (out of 21 possible) is close enough to show deviation from independent assortment; this is not a pair that Mendel studied. Some recent researchers have suggested that Fisher's criticisms of Mendel's work may have been exaggerated.[24][25]

See also

References

  1. ^ 20 July is his birthday; often mentioned is 22 July, the date of his baptism. Biography of Mendel at the Mendel Museum
  2. ^ "Gregor Mendel". 
  3. ^ "Mendel, Mendelism and Genetics". 
  4. ^ a b c Bowler, Peter J. (2003). Evolution: the history of an idea. Berkeley: University of California Press. ISBN 0-520-23693-9. 
  5. ^ Henig 2000, p. 24.
  6. ^ Gregor Mendel, Alain F. Corcos, Floyd V. Monaghan, Maria C. Weber "Gregor Mendel's Experiments on Plant Hybrids: A Guided Study", Rutgers University Press, 1993.
  7. ^ Henig 2000, pp. 19–21.
  8. ^ Hasan, Heather (2004). Mendel and The Laws Of Genetics. The Rosen Publishing Group. ISBN 9781404203099. 
  9. ^ a b Henig 2000, pp. 47–62.
  10. ^ a b c "The Mathematics of Inheritance". Online museum exhibition. The Masaryk University Mendel Museum. Retrieved 20 January 2010. 
  11. ^ a b c "Online Museum Exhibition". The Masaryk University Mendel Museum. Retrieved 20 January 2010. 
  12. ^ Henig 2000, pp. 15–17.
  13. ^ "The Enigma of Generation and the Rise of the Cell". The Masaryk University Mendel Museum. Retrieved 20 January 2010. 
  14. ^ "Mendel's Garden". The Masaryk University Mendel Museum. Retrieved 20 January 2010. 
  15. ^ Henig 2000, pp. 78–80.
  16. ^ Henig 2000, pp. 134–138.
  17. ^ Randy Moore (May 2001 vol=27). "The "Rediscovery" of Mendel's Work". Bioscene. 
  18. ^ Mendel, J.G. (1866). Versuche über Pflanzenhybriden Verhandlungen des naturforschenden Vereines in Brünn, Bd. IV für das Jahr, 1865 Abhandlungen:3–47. For the English translation, see: Druery, C.T and William Bateson (1901). "Experiments in plant hybridization". Journal of the Royal Horticultural Society 26: 1–32. Retrieved 9 October 2009. 
  19. ^ Windle, B.C.A.; Translated Looby, John (1911). "Mendel, Mendelism". Catholic Encyclopedia. Retrieved 2 April 2007. 
  20. ^ a b Carlson, Elof Axel (2004). "Doubts about Mendel's integrity are exaggerated". Mendel's Legacy. Cold Spring Harbor, NY: Cold Spring Harbor Laboratory Press. pp. 48–49. ISBN 978-0-87969-675-7. 
  21. ^ Mayr E. (1982). The Growth of Biological Thought. Cambridge: The Belknap Press of Harvard University Press. p. 730. ISBN 0-674-36446-5. 
  22. ^ Henig 2000, pp. 1–9.
  23. ^ Fisher, R. A. (1936). Has Mendel's work been rediscovered? Annals of Science 1:115–137.
  24. ^ Hartl, Daniel L.; Fairbanks, Daniel J. (1 March 2007). "Mud Sticks: On the Alleged Falsification of Mendel's Data". Genetics 175 (3): 975–979. PMC 1840063. PMID 17384156. "[The] allegation of deliberate falsification can finally be put to rest, because on closer analysis it has proved to be unsupported by convincing evidence." 
  25. ^ Novitski, Charles E. (March 2004). "On Fisher's criticism of Mendel's results with the garden pea". Genetics 166 (3): 1133–1136. doi:10.1534/genetics.166.3.1133. PMC 1470775. PMID 15082533. Retrieved 20 March 2010. "In conclusion, Fisher’s criticism of Mendel’s data—that Mendel was obtaining data too close to false expectations in the two sets of experiments involving the determination of segregation ratios—is undoubtedly unfounded." 

Bibliography

By Maria Malate about the Father of Genetics" Made by Gregor Mendel edit refutes allegations about "data smoothing"

  • James Walsh, Catholic Churchmen in Science, Philadelphia: Dolphin Press, 1906
  • Ronald A. Fisher, "Has Mendel's Work Been Rediscovered?" Annals of Science, Volume 1, (1936): 115–137. Discusses the possibility of fraud in his research.

Further reading

  • Punnett, Reginald Crundall (1922). "Mendelism". London: Macmillan.  (1st Pub. 1905)
  • Taylor, Monica (July–September 1922). "Abbot Mendel". Dublin Review (London: Burns, Oates and Washbourne). 
  • Windle, Bertram C. A. (1915). "Mendel and His Theory of Heredity". A Century of Scientific Thought and Other Essays. Burns & Oates. 

External links