Editing Dominance (genetics) (section)

==Background==
{{See also|Introduction to genetics}}
[[File:Journal of Agricultural Research (1917) (14582377398).jpg|thumb|240px|Inheritance of dwarfing in maize. Demonstrating the heights of plants from the two parent variations and their F1 heterozygous hybrid (centre)]]

[[Gregor Johann Mendel]], "The Father of Genetics", promulgated the idea of dominance in the 1860s. However, it was not widely known until the early twentieth century. Mendel observed that, for a variety of traits of garden peas having to do with the appearance of seeds, seed pods, and plants, there were two discrete phenotypes, such as round versus wrinkled seeds, yellow versus green seeds, red versus white flowers or tall versus short plants.<ref name=":8" /> When bred separately, the plants always produced the same phenotypes, generation after generation. However, when lines with different phenotypes were crossed (interbred), one and only one of the parental phenotypes showed up in the offspring (green, round, red, or tall).<ref name=":8" /> However, when these [[Hybrid (biology)|hybrid]] plants were crossed, the offspring plants showed the two original phenotypes, in a characteristic 3:1 ratio, the more common phenotype being that of the parental hybrid plants. Mendel reasoned that each parent in the first cross was a homozygote for different alleles (one parent AA and the other parent aa), that each contributed one allele to the offspring, with the result that all of these hybrids were heterozygotes (Aa), and that one of the two alleles in the hybrid cross dominated expression of the other: A masked a. The final cross between two heterozygotes (Aa X Aa) would produce AA, Aa, and aa offspring in a 1:2:1 genotype ratio with the first two classes showing the (A) phenotype, and the last showing the (a) phenotype, thereby producing the 3:1 phenotype ratio.<ref name=":8" />

Mendel did not use the terms gene, allele, phenotype, genotype, homozygote, and heterozygote, all of which were introduced later.<ref name=":9" /><ref name=":10">{{Cite web |title=1909: The Word Gene Coined |url=https://www.genome.gov/25520244/online-education-kit-1909-the-word-gene-coined |access-date=2025-04-27 |website=www.genome.gov |language=en}}</ref> He did introduce the notation of capital and lowercase letters for dominant and recessive alleles, respectively, still in use today.

In 1928, British population geneticist [[Ronald Fisher]] proposed that dominance acted based on natural selection through the contribution of [[modifier genes]].<!--[[natural selection]] was first proposed by the British population geneticist [[Ronald Fisher]] in 1928,<ref>Fisher, R.A. 1928. [http://digital.library.adelaide.edu.au/coll/special//fisher/68.pdf The possible modification of the response of the wild type to recurrent mutations] {{webarchive |url=https://web.archive.org/web/20090218135035/http://digital.library.adelaide.edu.au/coll/special/ |date=February 18, 2009 }}. Am. Nat., 62: 115–126.</ref> and expanded upon in his book ''[[The Genetical Theory of Natural Selection]]''.<ref>Fisher, R.A. 1930. ''The Genetical Theory of Natural Selection'', Clarendon Press, Oxford</ref>  However, [[Sewall Wright]] and [[J.B.S. Haldane]] believed that the main explanation for dominance should be based on--> In 1929, American geneticist [[Sewall Wright]] responded by stating that dominance is simply a physiological consequence of metabolic pathways and the relative necessity of the gene involved.<ref name=":9">Mayo, O. and Bürger, R. 1997. [http://journals.cambridge.org/action/displayAbstract?fromPage=online&aid=637 The evolution of dominance: A theory whose time has passed?] {{Webarchive|url=https://web.archive.org/web/20160304073242/http://journals.cambridge.org/action/displayAbstract?fromPage=online&aid=637 |date=2016-03-04 }} "Biological Reviews", Volume 72, Issue 1, pp. 97–110</ref><ref>Bourguet, D. 1999. [http://www.nature.com/hdy/journal/v83/n1/full/6885600a.html The evolution of dominance] {{Webarchive|url=https://web.archive.org/web/20160829172824/http://www.nature.com/hdy/journal/v83/n1/full/6885600a.html |date=2016-08-29 }} ''Heredity'', Volume 83, Number 1, pp. 1–4</ref><ref name=":10" />