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{{for|the Japanese lexical law|Ōno's lexical law}}

'''Ohno's law''' was proposed by a Japanese-American biologist [[Susumu Ohno]], saying that the [[gene]] content of the [[mammal]]ian [[species]] has been conserved over species not only in the [[DNA]] content but also in the genes themselves. That is, nearly all mammalian species have conserved the [[X chromosome]] from their primordial X chromosome of a common ancestor.<ref name=Ohno67>Ohno S (1967). ''Sex Chromosomes and sex-linked genes.'' Berlin:Springer-Verlag.</ref>

== Evidence ==
Mammalian X chromosomes in various species, including [[human]] and [[mouse]], have nearly the same size, with the content of about 5% of the genome. Additionally, for individual [[Locus (genetics)|gene loci]], a number of X-linked genes are common through mammalian species. Examples include [[glucose-6-phosphate dehydrogenase]] (G6PD), and the genes for [[Factor VIII]] and [[Factor IX]]. Moreover, no instances were found where an [[Sex linkage|X-linked]] gene in one species was located on an [[autosome]] in the other species.<ref name=Ohno67 />

== Conservation mechanisms ==
The content of a chromosome would be changed mainly by mutation after duplication of the chromosome and translocation with other chromosomes. However, in mammals, since the chromosomal [[Sex-determination system|sex-determination]] mechanism would have been established in their earlier stages of [[evolution]], [[polyploidy]] would have not occurred due to its incompatibility with the sex-determining mechanism. Moreover, X-autosome [[Chromosomal translocation|translocation]] would have been prohibited because it might have resulted in detrimental effects for survival to the organism. Thus in mammals, the content of X chromosomes has been conserved after typical 2 round duplication events at early ancestral stages of evolution, at the fish or amphibia ([[2R hypothesis]]).<ref name=Ohno67 /><ref name=Ohno70>Ohno S (1970). ''Evolution by Gene Duplication.'' London: Allen and Unwin, {{ISBN|0-04-575015-7}}.</ref>

== Contradicting and supportive evidence ==
Genes on the long arm of the human X are contained in the monotreme X and genes on the short arm of the human X are distributed on the autosomes of marsupials.<ref name=Watson>Watson JM, Riggs A, Graves JA (1992). "Gene mapping studies confirm the homology between the platypus X and echidna X1 chromosomes and identify a conserved ancestral monotreme X chromosome". ''Chromosoma'' 101(10): 596–601, {{PMID|1424984}}.</ref> Ohno commented to the result that [[monotreme]]s and [[marsupial]]s were not considered to be ancestors of true mammals, but they have diverged very early from the main line of mammals.<ref name=Ohno93>Ohno S (1993). "Patterns in genome evolution". ''Curr Opin Genet Dev'' 3(6): 911–914, {{PMID|8118217}}.</ref>

By comparison, [[Chloride channel]] gene (''CLCN4'') was mapped to the human X but on chromosome 7 of C57BL/6 mice, species of [[House Mouse|''Mus musculus'']], though the gene is located on X of [[Algerian Mouse|''Mus spretus'']] and [[rat]].<ref name=Palmer>Palmer S, Perry J, Ashworth A (1995). "A contravention of ohno's law in mice". ''Nat Genet'' 10(4): 472–476, {{PMID|7670497}}, {{doi|10.1038/ng0895-472}}.</ref>

== Dictionary entries ==
* Rédei GP (2003). "Ohno's law." ''Encyclopedic dictionary of genetics, genomics, and proteomics, 2nd ed.'' New York: Wiley-Liss, p. 870. {{ISBN|0-471-26821-6}}.

== References ==
{{reflist}}

[[Category:History of biology]]
[[Category:Biology theories]]
[[Category:Genetics]]
[[Category:Evolutionary biology]]

Ohno's law - История изменений

Admin: 1 версия импортирована

ru>Bearian: /* Contradicting and supportive evidence */By comparison,