Editing Gregor Mendel (section)

=== Experiments on plant hybridization ===
{{Main|Mendelian inheritance}}
[[File:Mendelian inheritance.svg|thumb|Dominant and recessive phenotypes. (1) Parental generation. (2) F1 generation. (3) F2 generation.]]
Mendel, known as the "father of modern genetics," chose to study variation in plants in his monastery's {{convert|2|ha|acre}} experimental garden.<ref>{{cite web |url=https://mendel-museum.com/mendels-experiments-on-peas/ |title=Mendel's Experiments on Peas |publisher=The Masaryk University Mendel Museum |access-date=4 October 2020 |archive-date=9 August 2021 |archive-url=https://web.archive.org/web/20210809014930/https://mendel-museum.com/mendels-experiments-on-peas/ |url-status=dead }}</ref> Mendel was assisted in his experimental design by Aleksander Zawadzki while his superior abbot [[Cyril Napp|Napp]] wrote to discourage him, saying that the Bishop giggled when informed of the detailed genealogies of peas.<ref>{{Cite journal |last=Szybalski |first=W. |date=2010 |title=Professor Alexander Zawadzki of Lviv University – Gregor Mendel's mentor and inspirer |journal=Biopolymers and Cell |volume=26 |issue=2 |pages=83–86 |doi=10.7124/bc.000149|doi-access=free }}</ref>

After initial experiments with pea plants, Mendel settled on studying seven traits that seemed to be inherited 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.{{sfn|Henig|2000|pp=78–80}} Between 1856 and 1863 Mendel cultivated and tested some 28,000 plants, the majority of which were [[pea]] plants (''[[Pisum sativum]]'').<ref>{{cite book|last1=Magner|first1=Lois N. |title=History of the Life Sciences|year=2002 |publisher=Marcel Dekker |location=New York|isbn=978-0-203-91100-6|page=380|edition=3, revised|url=https://books.google.com/books?id=YKJ6gVYbrGwC&pg=PA380}}</ref><ref>{{cite book|last1=Gros|first1=Franc̜ois|title=The Gene Civilization|year=1992|publisher=McGraw Hill|location=New York|isbn=978-0-07-024963-9|page=[https://archive.org/details/genecivilization00gros/page/28 28]|edition=English|url=https://archive.org/details/genecivilization00gros|url-access=registration}}</ref><ref name="Moore-2003">{{Cite journal|last=Moore |first=Randy |title=The "Rediscovery" of Mendel's Work |journal=Bioscene |year=2001 |volume=27 |issue=2 |pages=13–24 |url=https://www.cs.uml.edu/~grinstei/91.510/Rediscovery%20of%20Mendel.pdf |archive-url=https://web.archive.org/web/20160216153032/http://courses.pbsci.ucsc.edu/mcdb/bio105/Spring15/Lecture2/Rediscovery%20of%20Mendel.pdf |archive-date=16 February 2016 }}</ref> This study showed that, when true-breeding different varieties were crossed to each other (e.g., tall plants fertilized by short plants), in the second generation, one in four pea plants had [[purebred]] [[recessive]] [[Phenotypic trait|traits]], two out of four were [[hybrid (biology)|hybrids]], and one out of four were purebred [[dominance (genetics)|dominant]]. His experiments led him to make two generalizations, the [[Law of Segregation]] and the [[Law of independent assortment|Law of Independent Assortment]], which later came to be known as Mendel's Laws of Inheritance.<ref>{{cite book|last1=Butler |first1=John M.|title=Fundamentals of Forensic DNA Typing|date=2010|publisher=Elsevier/Academic Press|location=Burlington, MA|isbn=978-0-08-096176-7|pages=34–35|url=https://books.google.com/books?id=-OZeEmqzE4oC&pg=PA34}}</ref>

==== Initial reception of Mendel's work ====
Mendel presented his paper, {{lang|de|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.{{sfn|Henig|2000|pp=134–138}} It generated a few favorable reports in local newspapers,<ref name="Moore-2003" /> but was ignored by the scientific community. When Mendel's paper was published in 1866 in {{lang|de|[[Proceedings of the Natural History Society of Brünn|Verhandlungen des naturforschenden Vereines in Brünn]]}},<ref>Mendel, J.G. (1866). "[https://www.biodiversitylibrary.org/item/124139#page/133/mode/1up Versuche über Pflanzenhybriden]", ''Verhandlungen des naturforschenden Vereines in Brünn'', Bd. IV für das Jahr, 1865, ''Abhandlungen'': 3–47. For the English translation, see: {{cite journal|last1=Druery|first1=C.T.|last2=Bateson|first2=William|year=1901|title=Experiments in plant hybridization|url=http://www.esp.org/foundations/genetics/classical/gm-65.pdf |archive-url=https://web.archive.org/web/20000902033224/http://www.esp.org/foundations/genetics/classical/gm-65.pdf |archive-date=2000-09-02 |url-status=live|journal=Journal of the Royal Horticultural Society|volume=26|pages=1–32|access-date=9 October 2009}}</ref> it was seen as essentially about hybridization rather than inheritance, had little impact, and was cited only about three times over the next thirty-five years. His paper was criticized then but is now considered a seminal work.<ref>{{cite journal|last1=Galton|first1=D. J.|title=Did Mendel falsify his data?|journal=QJM|date=2011|volume=105|issue=2|pages=215–16|doi= 10.1093/qjmed/hcr195|pmid=22006558|doi-access=free}}</ref> Notably, [[Charles Darwin]] was not aware of Mendel's paper, and it is envisaged that if he had been aware of it, genetics as it exists now might have taken hold much earlier.<ref>{{cite journal|last1=Lorenzano|first1=P|title=What would have happened if Darwin had known Mendel (or Mendel's work)?|journal=History and Philosophy of the Life Sciences|date=2011|volume=33|issue=1|pages=3–49|pmid=21789954}}</ref><ref>{{cite journal|last1=Liu|first1=Y|title=Darwin and Mendel: who was the pioneer of genetics?|journal=Rivista di Biologia|date=2005|volume=98|issue=2|pages=305–22|pmid=16180199}}</ref> Mendel's scientific biography thus provides an example of the failure of obscure, highly original innovators to receive the attention they deserve.<ref name=":2">{{Cite journal|date=1995|title=The Plight of the Obscure Innovator in Science|journal=Social Studies of Science|volume=25|issue=1|pages=165–83|doi=10.1177/030631295025001008 |last1=Nissani |first1=M.|s2cid=144949936}}</ref>

==== Rediscovery of Mendel's work ====
About forty scientists listened to Mendel's two groundbreaking lectures, but it would appear that they failed to understand the implications of his work. Later, he also carried on a correspondence with [[Carl Nägeli]], one of the leading biologists of the time, but Nägeli also failed to appreciate Mendel's discoveries. At times, Mendel must have entertained doubts about his work, but not always: "My time will come," he reportedly told a friend,<ref name=":0" /> Gustav von Niessl.<ref name=":5">{{Cite journal|last=Gustafsson|first=A.|date=1969|title=The life of Gregor Johann Mendel--tragic or not?|journal=Hereditas|volume=62|issue=1|pages=239–258|doi=10.1111/j.1601-5223.1969.tb02232.x|pmid=4922561|doi-access=free}}</ref>

During Mendel's lifetime, most biologists held the idea that all characteristics were passed to the next generation through [[blending inheritance]] (indeed, many effectively are), in which the traits from each parent are averaged.<ref>{{Cite journal|last=Weldon|first=W. F. R.|date=1902|title=Mendel's Laws of Alternative Inheritance in Peas|url=https://academic.oup.com/biomet/article-lookup/doi/10.1093/biomet/1.2.228|journal=Biometrika|volume=1|issue=2|pages=228–233|doi=10.1093/biomet/1.2.228}}</ref><ref>{{Cite journal|last=Bulmer|first=Michael|date=1999|title=The Development of Francis Galton's Ideas on the Mechanism of Heredity|url=http://link.springer.com/10.1023/A:1004608217247|journal=Journal of the History of Biology|volume=32|issue=2|pages=263–292|doi=10.1023/A:1004608217247|pmid=11624207|s2cid=10451997}}</ref> Instances of this phenomenon are now explained by the action of multiple genes with [[Quantitative genetics|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.<ref name="Moore-2003" />

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.<ref name="Moore-2003" /> Though [[Erich von Tschermak]] was originally also credited with rediscovery, this is no longer accepted because he did not understand [[Mendelian inheritance|Mendel's laws]].<ref>{{cite book |author=Mayr E. |author-link=Ernst Mayr |year=1982 |title=The Growth of Biological Thought |location=Cambridge |publisher=The Belknap Press of Harvard University Press |isbn=978-0-674-36446-2 |page=730}}</ref> Though de Vries later lost interest in Mendelism, other biologists started to establish modern genetics as a science. All three of these researchers, each from a different country, published their rediscovery of Mendel's work within a two-month span in the spring of 1900.{{sfn|Henig|2000|pp=1–9}}

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 [[genotype|genotypic]] understanding of heredity, which they felt was lacking in previous studies of heredity, which had focused on [[phenotype|phenotypic]] approaches.<ref>{{Cite book|title=Mendel's Legacy: The Origins of Classical Genetics|last=Carlson|first=Elof Axel|publisher=Cold Spring Harbor|year=2004|location=New York}}</ref> Most prominent of these previous approaches was the [[Biostatistics|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 20th century, with the biometricians claiming statistical and mathematical rigor,<ref>{{cite journal|last1=Deichmann|first1=Ute|title=Early 20th-century research at the interfaces of genetics, development, and evolution: Reflections on progress and dead ends|journal=Developmental Biology|date=2011|volume=357|issue=1|pages=3–12|doi=10.1016/j.ydbio.2011.02.020 |pmid=21392502|doi-access=free}}</ref> whereas the Mendelians claimed a better understanding of biology.<ref>{{cite journal|last1=Elston|first1=RC|last2=Thompson|first2=EA|author2-link= Elizabeth A. Thompson |title=A century of biometrical genetics|journal=Biometrics|date=2000|volume=56|issue=3|pages=659–66|pmid=10985200|doi=10.1111/j.0006-341x.2000.00659.x|s2cid=45142547}}</ref><ref>{{cite journal|last1=Pilpel|first1=Avital|title=Statistics is not enough: revisiting Ronald A. Fisher's critique (1936) of Mendel's experimental results (1866)|journal=Studies in History and Philosophy of Science Part C: Studies in History and Philosophy of Biological and Biomedical Sciences|date=September 2007|volume=38|issue=3|pages=618–26|doi=10.1016/j.shpsc.2007.06.009 |pmid=17893069}}</ref> Modern genetics shows that Mendelian heredity is, in fact, an inherently biological process, though not all genes of Mendel's experiments are yet understood.<ref>{{Cite journal|last1=Reid|first1=J. B.|last2=Ross|first2=J. J.|title=Mendel's genes: toward a full molecular characterization|journal=Genetics|date=2011|volume=189|issue=1|pages=3–10|doi=10.1534/genetics.111.132118|pmid=21908742|pmc=3176118}}</ref><ref>{{cite journal|last1=Ellis|first1=T.H. Noel|last2=Hofer|first2=Julie M.I.|last3=Timmerman-Vaughan|first3=Gail M.|last4=Coyne|first4=Clarice J.|last5=Hellens|first5=Roger P.|title=Mendel, 150 years on|journal=Trends in Plant Science|date=2011|volume=16|issue=11|pages=590–96|doi=10.1016/j.tplants.2011.06.006|pmid=21775188|bibcode=2011TPS....16..590E }}</ref>

Ultimately, 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 (20th century)|modern synthesis]] of [[evolutionary biology]].<ref>{{cite journal|last1=Kutschera |first1=Ulrich|last2=Niklas|first2=KarlJ.|title=The modern theory of biological evolution: an expanded synthesis|journal=Naturwissenschaften|date=2004|volume=91|issue=6|pages=255–76|doi=10.1007/s00114-004-0515-y|pmid=15241603|bibcode=2004NW.....91..255K|s2cid=10731711}}</ref><ref>{{cite book|last1=Hall|first1=Brian Keith|last2=Hallgrímsson|first2=Benedikt|last3=Strickberger |first3=Monroe W.|title=Strickberger's evolution|date=2014|publisher=Jones & Bartlett Learning|location=Burlington, Mass.|isbn=978-1-4496-1484-3|pages=10–11|edition=5|url=https://books.google.com/books?id=WkcvuVpzjYQC}}</ref>

In the [[Soviet Union]] and China, Mendelian genetics was rejected in favor of [[Lamarckism]], leading to imprisonment and even execution of Mendelian geneticists (see [[Lysenkoism]]).