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<p><b>Новая страница</b></p><div>{{Short description|Effect when genes source into a phenotype}}<br />
{{Expand language|topic=|langcode=hu|otherarticle=Összeadódó hatású gének|date=June 2019}}<br />
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[[File:Fisher's_Polygenic_Model.png|thumb|This model illustrates polygenic additive effects on phenotype]]<br />
Genetic effects are broadly divided into two categories: additive and non-additive. '''Additive genetic effects''' occur where expression of more than one gene contributes to [[phenotype]] (or where [[Allele|alleles]] of a [[Zygosity|heterozygous]] gene both contribute), and the phenotypic expression of these gene(s) can be said to be the sum of these contributions.<br />
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Non-additive effects involve [[Dominance (genetics)|dominance]] or [[epistasis]], and cause outcomes that are not a sum of the contribution of the genes involved.<br />
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Additive genetic effects are singularly important with regard to [[Complex traits|quantitative traits]], as the sum of these effects informs the placement of a trait on the spectrum of possible outcomes. Quantitative traits are commonly polygenic (resulting from the effects of more than one [[Locus (genetics)|locus]]).<br />
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== Heritability ==<br />
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=== Broad sense heritability ===<br />
Variation in phenotypes across a population arises from the interaction between environmental variation and genetic variation between individuals. This can be stated mathematically as:<br />
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V<sub>P</sub> = V<sub>E</sub> + V<sub>G</sub>, where the terms refer to variation in phenotype, environment, and genotype respectively.<ref>{{Cite book |last1=Allendorf |first1=Frederick William |title=Conservation and the genomics of populations |last2=Funk |first2=W. Chris |last3=Aitken |first3=Sally N. |last4=Byrne |first4=Margaret |last5=Luikart |first5=Gordon |last6=Antunes |first6=Agostinho |date=2022 |publisher=Oxford University Press |isbn=978-0-19-885656-6 |edition=Third |location=New York, NY}}</ref><br />
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Broad sense heritability (H<sup>2</sup>, or H<sub>B</sub>) refers to the phenotypic differences arising from all genetic effects, and can be described as the ratio of genotypic variation to that of phenotypic variation in the population, or: H<sup>2</sup> = V<sub>G</sub> / V<sub>P</sub>.<br />
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The genotypic variation from the above equation can be subdivided into V<sub>A</sub> (additive effects), V<sub>D</sub> (dominance effects), and V<sub>I</sub> (epistatic effects).<br />
[[File:Fisher's_Fundamental_Theorem.png|thumb|Visualization of the decreasing variation of additive effects to mean fitness over generations.]]<br />
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=== Narrow Sense Heritability ===<br />
Narrow sense Heritability (h<sup>2</sup> or H<sub>N</sub>) focuses specifically on the ratio of additive variance (V<sub>A</sub>) to total phenotypic variance (V<sub>P</sub>), or: h<sup>2</sup> = V<sub>A</sub> / V<sub>P.</sub><br />
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In the study of Heritability, Additive genetic effects are of particular interest in the fields of [[Conservation biology|Conservation]], and [[Selective breeding|Artificial selection]]. The effects of dominance and epistasis are not reliably transmitted to progeny (see [[Mendelian inheritance]], laws of segregation and independent assortment). This means that h<sup>2</sup> represents the phenotypic variation that is reliably passed from one generation to the next and which can be used to predict changes in mean fitness between generations. <ref>{{Cite book |last=Hartl |first=Daniel L. |title=Essential genetics and genomics |date=2018 |publisher=Jones & Bartlett Learning |isbn=978-1-284-15245-6 |edition=Seventh |location=Burlington, MA}}</ref><br />
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== Fisher's Fundamental Theorem ==<br />
[[Fisher's fundamental theorem of natural selection|Fisher's Fundamental Theorem]] asserts a direct correlation between the amount of genetic variation in a population and the possible variation in mean fitness for that population. This Theorem suggests that where a trait affects individual fitness, the amount of variation due to additive genetic effects will decline with each successive generation, and all other things being equal, will approach zero.<br />
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==References==<br />
{{Reflist}}<br />
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{{DEFAULTSORT:Additive Genetic Effects}}<br />
[[Category:Genetics]]<br />
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{{Genetics-stub}}</div>ru>Cmr08