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Pleiotropy
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==History== Pleiotropic traits had been previously recognized in the scientific community but had not been experimented on until [[Gregor Mendel]]'s 1866 pea plant experiment. Mendel recognized that certain pea plant traits (seed coat color, flower color, and axial spots) seemed to be inherited together;<ref name="Stearns-2016">{{Cite journal|last=Stearns|first=Frank W.|date=2016-11-15|title=One Hundred Years of Pleiotropy: A Retrospective |journal=Genetics |volume=186 |issue=3 |pages=767–773 |doi=10.1534/genetics.110.122549 |pmc=2975297 |pmid=21062962}}</ref> however, their [[Correlation and dependence|correlation]] to a single gene has never been proven. The term "pleiotropie" was first coined by [[Ludwig Plate]] in his [[Festschrift]], which was published in 1910.<ref name="Stearns-2016">{{Cite journal|last=Stearns|first=Frank W.|date=2016-11-15|title=One Hundred Years of Pleiotropy: A Retrospective |journal=Genetics |volume=186 |issue=3 |pages=767–773 |doi=10.1534/genetics.110.122549 |pmc=2975297 |pmid=21062962}}</ref> He originally defined pleiotropy as occurring when "several characteristics are dependent upon ... [inheritance]; these characteristics will then always appear together and may thus appear correlated".<ref>{{Cite journal|last=McKusick|first=V A |date=1976-05-01 |title=Letter: Pleiotropism.|journal=American Journal of Human Genetics|volume=28|issue=3|pages=301–302 |pmc=1685011|pmid=1266859}}</ref> This definition is still used today. After Plate's definition, [[Hans Grüneberg|Hans Gruneberg]] was the first to study the [[Mechanism (biology)|mechanisms]] of pleiotropy.<ref name="Stearns-2016" /> In 1938 Gruneberg published an article dividing pleiotropy into two distinct types: "genuine" and "spurious" pleiotropy. "Genuine" pleiotropy is when two distinct primary products arise from one [[Locus (genetics)|locus]]. "Spurious" pleiotropy, on the other hand, is either when one primary product is utilized in different ways or when one primary product initiates a cascade of events with different [[Phenotype|phenotypic]] consequences. Gruneberg came to these distinctions after experimenting on rats with skeletal [[mutation]]s. He recognized that "spurious" pleiotropy was present in the mutation, while "genuine" pleiotropy was not, thus partially invalidating his own original [[theory]].<ref>Gruneberg, H., 1938 An analysis of the "pleiotropic" effects of a new lethal mutation in the rat (Mus norvegicus). Proc. R. Soc. Lond. B 125: 123–144.</ref> Through subsequent [[research]], it has been established that Gruneberg's definition of "spurious" pleiotropy is what we now identify simply as "pleiotropy".<ref name="Stearns-2016" /> In 1941 American geneticists [[George Beadle]] and [[Edward Tatum]] further invalidated Gruneberg's definition of "genuine" pleiotropy, advocating instead for the [[One gene-one enzyme hypothesis|"one gene-one enzyme" hypothesis]] that was originally introduced by French biologist [[Lucien Cuénot]] in 1903.<ref name="Stearns-2016" /><ref>{{cite journal |last1=Beadle |first1=G. W. |last2=Tatum |first2=E. L. |title=Genetic Control of Biochemical Reactions in Neurospora |journal=Proceedings of the National Academy of Sciences |date=15 November 1941 |volume=27 |issue=11 |pages=499–506 |doi=10.1073/pnas.27.11.499 |pmid=16588492 |pmc=1078370 |bibcode=1941PNAS...27..499B |doi-access=free }}</ref> This hypothesis shifted future research regarding pleiotropy towards how a single gene can produce various phenotypes. In the mid-1950s [[Richard Goldschmidt]] and [[Ernst Hadorn]], through separate individual research, reinforced the faultiness of "genuine" pleiotropy. A few years later, Hadorn partitioned pleiotropy into a "mosaic" model (which states that one locus directly affects two phenotypic traits) and a "relational" model (which is analogous to "spurious" pleiotropy). These terms are no longer in use but have contributed to the current understanding of pleiotropy.<ref name="Stearns-2016" /> By accepting the one gene-one enzyme hypothesis, scientists instead focused on how uncoupled phenotypic traits can be affected by [[genetic recombination]] and mutations, applying it to [[Population biology|populations]] and [[evolution]].<ref name="Stearns-2016" /> This view of pleiotropy, "universal pleiotropy", defined as locus mutations being capable of affecting essentially all traits, was first implied by [[Ronald Fisher]]'s [[Fisher's geometric model|Geometric Model]] in 1930. This mathematical model illustrates how evolutionary [[Fitness (biology)|fitness]] depends on the independence of phenotypic variation from random changes (that is, mutations). It theorizes that an increasing phenotypic independence corresponds to a decrease in the likelihood that a given mutation will result in an increase in fitness.<ref>{{Cite journal |last=Edwards |first=A W |date=2016-11-15 |title=The genetical theory of natural selection |journal=Genetics |volume=154 |issue=4 |pages=1419–1426 |doi=10.1093/genetics/154.4.1419 |pmc=1461012 |pmid=10747041}}</ref> Expanding on Fisher's work, [[Sewall Wright]] provided more evidence in his 1968 book ''Evolution and the Genetics of Populations: Genetic and Biometric Foundations'' by using molecular genetics to support the idea of "universal pleiotropy". The concepts of these various studies on evolution have seeded numerous other research projects relating to individual fitness.<ref name="Paaby 66–73" /> In 1957 evolutionary biologist [[George C. Williams (biologist)|George C. Williams]] theorized that antagonistic effects will be exhibited during an organism's [[Biological life cycle|life cycle]] if it is closely linked and pleiotropic. [[Natural selection]] favors genes that are more beneficial prior to [[reproduction]] than after (leading to an increase in [[reproductive success]]). Knowing this, Williams argued that if only close [[Genetic linkage|linkage]] was present, then beneficial traits will occur both before and after reproduction due to natural selection. This, however, is not observed in nature, and thus [[Antagonistic pleiotropy hypothesis|antagonistic pleiotropy]] contributes to the slow deterioration with age ([[senescence]]).<ref>{{cite journal | last1 = Williams | first1 = G. C. | year = 1957 | title = Pleiotropy, natural selection, and the evolution of senescence | journal = Evolution | volume = 11 | issue = 4| pages = 398–411 | doi=10.2307/2406060| jstor = 2406060 }}</ref>
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