Editing Mendelian inheritance (section)

==History==
{{main|History of genetics}}

The principles of Mendelian inheritance were named for and first derived by [[Gregor Johann Mendel]],<ref name="Fairbanks-2001">{{Cite journal |last1=Fairbanks |first1=Daniel J. |last2=Rytting |first2=Bryce |date=May 2001 |title=Mendelian controversies: a botanical and historical review |url=https://bsapubs.onlinelibrary.wiley.com/doi/10.2307/2657027 |journal=American Journal of Botany |language=en |volume=88 |issue=5 |pages=737–752 |doi=10.2307/2657027 |jstor=2657027 |pmid=11353700 |issn=0002-9122|url-access=subscription }}</ref> a nineteenth-century [[Moravians|Moravian]] [[monk]] who formulated his ideas after conducting simple hybridization experiments with pea plants ''([[Pisum sativum]])'' he had planted in the garden of his monastery.<ref name="Henig-2000">{{Cite book |last=Henig |first=Robin Marantz |url=http://archive.org/details/monkingardenlost00heni |title=The monk in the garden : the lost and found genius of Gregor Mendel, the father of genetics |date=2000 |publisher=Boston : Houghton Mifflin |others=Internet Archive |isbn=978-0-395-97765-1}}</ref> Between 1856 and 1863, Mendel cultivated and tested some 5,000 pea plants. From these experiments, he induced two generalizations which later became known as ''Mendel's Principles of Heredity'' or ''Mendelian inheritance''. He described his experiments in a two-part paper, ''Versuche über Pflanzen-Hybriden'' (''[[Experiments on Plant Hybridization]]''),<ref>{{Cite book |last1=Mendel |first1=Gregor |url=https://www.biodiversitylibrary.org/bibliography/61004 |title=Versuche über Pflanzen-Hybriden |last2=Mendel |first2=Gregor |date=1866 |publisher=Im Verlage des Vereines |location=Brünn}}</ref> that he presented to the Natural History Society of [[Brno]] on 8 February and 8 March 1865, and which was published in 1866.<ref name="Fairbanks-2001" /><ref>{{Cite web |title=Mendel's Paper (English - Annotated) |url=http://www.mendelweb.org/Mendel.html |access-date=2024-03-23 |website=www.mendelweb.org}}</ref><ref>{{Citation |last=Mendel |first=Gregor |title=Versuche über Pflanzenhybriden |date=1970 |pages=21–64 |editor-last=Mendel |editor-first=Gregor |url=https://doi.org/10.1007/978-3-663-19714-0_4 |access-date=2024-03-23 |chapter= |chapter-url= |place=Wiesbaden |publisher=Vieweg+Teubner Verlag |language=de |doi=10.1007/978-3-663-19714-0_4 |isbn=978-3-663-19714-0}}</ref><ref>{{Cite journal |last1=Mielewczik |first1=Michael |last2=Moll-Mielewczik |first2=Janine |last3=Simunek |first3=Michal V. |last4=Hossfeld |first4=Uwe |date=2022-09-01 |title="Versuche über Pflanzen-Hybriden" — neue Einsichten |url=https://doi.org/10.1007/s12268-022-1820-8 |journal=BIOspektrum |language=de |volume=28 |issue=5 |pages=565 |doi=10.1007/s12268-022-1820-8 |issn=1868-6249|url-access=subscription }}</ref>

Mendel's results were at first largely ignored. Although they were not completely unknown to biologists of the time, they were not seen as generally applicable, even by Mendel himself, who thought they only applied to certain categories of species or traits. A major roadblock to understanding their significance was the importance attached by 19th-century biologists to the [[Blending inheritance|apparent blending]] of [[Complex traits|many inherited traits]] in the overall appearance of the progeny,{{cn|date=April 2024}} now known to be due to [[Quantitative trait locus|multi-gene interactions]], in contrast to the organ-specific binary characters studied by Mendel.<ref name="Henig-2000" /> In 1900, however, his work was "re-discovered" by three European scientists, [[Hugo de Vries]], [[Carl Correns]], and [[Erich von Tschermak]]. The exact nature of the "re-discovery" has been debated: De Vries published first on the subject, mentioning Mendel in a footnote, while Correns pointed out Mendel's priority after having read De Vries' paper and realizing that he himself did not have priority. De Vries may not have acknowledged truthfully how much of his knowledge of the laws came from his own work and how much came only after reading Mendel's paper. Later scholars have accused Von Tschermak of not truly understanding the results at all.<ref>{{cite journal | doi=10.1093/oxfordjournals.jhered.a110361 | title=Tschermak: A non-discoverer of Mendelism II. A critique | date=1987 | last1=Monaghan | first1=Floyd V. | last2=Corcos | first2=Alain F. | journal=Journal of Heredity | volume=78 | issue=3 | pages=208–210 | pmid=3302014 }}</ref><ref>{{Cite book |last=Simunek |first=Michal V. |title=The Mendelian Dioskuri. Correspondence of Armin with Erich von Tschermak-Seysenegg, 1898-1951. |date=January 2011 |publisher=Pavel Mervart & Institute of Contemporary History of the AcSc Prague |year=2011 |isbn=978-80-87378-67-0}}</ref>

Regardless, the "re-discovery" made Mendelism an important but controversial theory. Its most vigorous promoter in Europe was [[William Bateson]], who coined the terms "[[genetics]]" and "[[allele]]" to describe many of its tenets.<ref name="Goldschmidt-1951">{{Cite journal |last=Goldschmidt |first=Richard B. |date=1951-01-01 |title=Chromosomes and Genes |url=http://symposium.cshlp.org/content/16/1 |journal=Cold Spring Harbor Symposia on Quantitative Biology |language=en |volume=16 |pages=1–11 |doi=10.1101/SQB.1951.016.01.003 |issn=0091-7451 |pmid=14942726|url-access=subscription }}</ref> The model of [[heredity]] was contested by other biologists because it implied that heredity was discontinuous, in opposition to the apparently continuous variation observable for many traits.<ref>{{Cite journal |last=Sumner |first=Francis B. |date=1929 |title=Is Evolution a Continuous or Discontinuous Process? |url=https://www.jstor.org/stable/14824 |journal=The Scientific Monthly |volume=29 |issue=1 |pages=72–78 |jstor=14824 |issn=0096-3771}}</ref> Many biologists also dismissed the theory because they were not sure it would apply to all species. However, later work by biologists and statisticians such as [[Ronald Fisher]] showed that if multiple Mendelian factors were involved in the expression of an individual trait, they could produce the diverse results observed, thus demonstrating that Mendelian genetics is compatible with [[natural selection]].<ref name="Fisher-1999">{{Cite book |last=Fisher |first=Sir Ronald Aylmer |url=https://books.google.com/books?id=sT4lIDk5no4C&dq=ronald+fisher+genetic+diversity&pg=PR6 |title=The Genetical Theory of Natural Selection: A Complete Variorum Edition |date=1999-10-21 |publisher=OUP Oxford |isbn=978-0-19-850440-5 |language=en}}</ref><ref name="Fisher">{{Cite journal |last1=Fisher |first1=R. A. | date=1919|title=XV.—The Correlation between Relatives on the Supposition of Mendelian Inheritance.|journal=Earth and Environmental Science Transactions of the Royal Society of Edinburgh|volume=52|issue=2|pages=399–433|doi=10.1017/S0080456800012163 |s2cid=181213898 | url=https://zenodo.org/record/1428666}}</ref> [[Thomas Hunt Morgan]] and his assistants later integrated Mendel's theoretical model with the [[chromosome]] theory of inheritance, in which the chromosomes of [[Cell (biology)|cells]] were thought to hold the actual hereditary material, and created what is now known as [[classical genetics]], a highly successful foundation which eventually cemented Mendel's place in history.<ref name="Fairbanks-2001" /><ref name="Goldschmidt-1951" />

Mendel's findings allowed scientists such as Fisher and [[J.B.S. Haldane]] to predict the expression of traits on the basis of mathematical probabilities. An important aspect of Mendel's success can be traced to his decision to start his crosses only with plants he demonstrated were [[True-breeding organism|true-breeding]].<ref name="Henig-2000" /><ref name="Fisher-1999" /> He only measured discrete (binary) characteristics, such as color, shape, and position of the seeds, rather than quantitatively variable characteristics. He expressed his results numerically and subjected them to [[Statistics#Statistical methods|statistical analysis]]. His method of data analysis and his large [[sample size]] gave credibility to his data. He had the foresight to follow several successive generations (P, F<sub>1</sub>, F<sub>2</sub>, F<sub>3</sub>) of pea plants and record their variations. Finally, he performed "test crosses" ([[backcrossing]] descendants of the initial [[Hybridization (biology)|hybridization]] to the initial true-breeding lines) to reveal the presence and proportions of [[recessive]] characters.<ref>{{Cite web |title=Gregor Mendel and the Principles of Inheritance {{!}} Learn Science at Scitable |url=http://www.nature.com/scitable/topicpage/gregor-mendel-and-the-principles-of-inheritance-593 |access-date=2024-03-23 |website=www.nature.com |language=en}}</ref>