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Experiments on Plant Hybridization

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"Experiments on Plant Hybridization" (German: Versuche über Pflanzen-Hybriden) is a seminal paper written in 1865 and published in 1866[1][2] by Gregor Mendel, an Augustinian friar considered to be the founder of modern genetics. The paper was the result after years spent studying genetic traits in Pisum sativum, the pea plant.

Content

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In his paper, Mendel compared 7 pairs of discrete traits found in a pea plant:

Characteristics Contrasting traits Offspring traits
Flower Color Violet and White Violet
Flower Position Axial and Terminal Axial
Plant Height Tall and Dwarf Tall
Seed Texture Round and Wrinkled Round
Seed Color Green and Yellow Yellow
Pea Pod Texture Inflated and Constricted Inflated
Pea Pod Color Green and Yellow Green

Through experimentation, Mendel discovered that one inheritable trait would invariably be dominant to its recessive alternative. Mendel laid out the genetic model later known as Mendelian inheritance or Mendelian genetics. This model provided an alternative to blending inheritance, which was the prevailing theory at the time.

History

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Mendel read his paper to the Natural History Society of Brünn. It was published in the Proceedings of the Natural History Society of Brünn the following year.

Mendel's work received little attention from the scientific community and was largely forgotten. It was not until the early 20th century that Mendel's work was rediscovered and his ideas used to help form the modern synthesis.

Analysis

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In 1936, the statistician Ronald Fisher used a Pearson's chi-squared test to analyze Mendel's data and concluded that Mendel's results with the predicted ratios were far too perfect, suggesting that adjustments (intentional or unconscious) had been made to the data to make the observations fit the hypothesis.[3]

Later authors have suggested Fisher's analysis was flawed, proposing various statistical and botanical explanations for Mendel's numbers.[4] It is also possible that Mendel's results are "too good" merely because he reported the best subset of his data—Mendel mentioned in his paper that the data were from a subset of his experiments.

Modern geneticists have inferred the 7 genes studied by Mendel. It is impossible to know for certain, but the identification is possible to a high degree of confidence based on Mendel's description, and the pea varieties grown in central Europe in the 1850s.[5] The table shows that the 7 genes appeared on 5 chromosomes. Of these, the only pair with significant linkage are V and LE, who are 12.6 map units apart. The other pair, R and GP, are very weakly linked. The effect is that Mendel was unlikely to have encountered genetic linkage. In any case, he did not report dihybrid experiments on either of these pairs, and only reported on the unlinked pairs, and he always found the ratio to be 9:3:3:1.[6]

Genes involved in seven pea traits studied by Mendel[5]
Trait Dominant phenotype Recessive phenotype Symbol group Linkage group Cloned? Gene function Molecular nature of mutation
Seed shape Round Wrinkled R V Yes Starch branching enzyme 1 0.8-kb insertion
Stem length Tall Dwarf LE III Yes GA 3-oxidase1 G-to-A substitution
Cotyledon color Yellow Green I I Yes Stay-green gene 6-bp insertion
Seed coat/flower color Purple White A II Yes bHLH transcription factor G-to-A at splice site
Pod color Green Yellow GP V No Chloroplast structure in pod wall Unknown
Pod form Inflated Constricted V III No Sclerenchyma formation in pods Unknown
Position of flowers Axial Terminal FA IV No Meristem function Unknown
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The full text of Experiments in Plant-Hybridisation at Wikisource

References

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  1. ^ Mendel, J. G. (1866). "Versuche über Pflanzenhybriden", Verhandlungen des naturforschenden Vereines in Brünn, Bd. IV für das Jahr, 1865, Abhandlungen: 3–47, [1]. For the English translation, see: Druery, C. T.; Bateson, William (1901). "Experiments in plant hybridization" (PDF). Journal of the Royal Horticultural Society. 26: 1–32. Retrieved 9 October 2009.
  2. ^ "Mendel's paper "Versuche über Pflanzenhybriden", was read at meetings of the Brunn Natural History Society on 8th February and 8th March 1865, and was published in the Verhandlungen des naturforschenden Vereines in Brünn, 4, 1865, which appeared in 1866" (Gregor Mendel, Experiments in Plant Hybridisation, Cosimo, Inc., 2008, p. 7).
  3. ^ Fisher, R. A. (1936). "Has Mendel's work been rediscovered?". Annals of Science. 1 (2): 115–126. doi:10.1080/00033793600200111. hdl:2440/15123.
  4. ^ Sturtevant, A. H. (2001). A History of Genetics. Cold Springs Harbor, New York: Cold Springs Harbor Laboratory Press. pp. 13–16. ISBN 0-87969-607-9.
  5. ^ a b Reid, James B.; Ross, John J. (September 2011). "Mendel's Genes: Toward a Full Molecular Characterization". Genetics. 189 (1): 3–10. doi:10.1534/genetics.111.132118. ISSN 0016-6731. PMC 3176118. PMID 21908742.
  6. ^ Meneely, Philip Mark; Dawes Hoang, Rachel; Okeke, Iruka N.; Heston, Katherine (2017). Genetics: genes, genomes, and evolution. Oxford: Oxford University Press. p. 349. ISBN 978-0-19-879536-0. OCLC 951645141.