Editing Quantitative genetics (section)

{{short description|Study of the inheritance of continuously variable traits}}
{{cleanup|date=February 2024|reason=nested fractions probably better written with {{tag|math}} markup}}
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'''Quantitative genetics''' is the study of [[quantitative trait]]s, which are [[phenotype]]s that vary continuously—such as height or mass—as opposed to phenotypes and gene-products that are [[Categorical variable|discretely identifiable]]—such as eye-colour, or the presence of a particular biochemical.

Both of these branches of [[genetics]] use the frequencies of different [[allele]]s of a [[gene]] in breeding populations (gamodemes), and combine them with concepts from simple [[Mendelian inheritance]] to analyze inheritance patterns across generations and descendant lines. While [[population genetics]] can focus on particular genes and their subsequent metabolic products, quantitative genetics focuses more on the outward phenotypes, and makes only summaries of the underlying genetics.

Due to the continuous distribution of phenotypic values, quantitative genetics must employ many other statistical methods (such as the ''effect size'', the ''mean'' and the ''variance'') to link phenotypes (attributes) to genotypes. Some phenotypes may be analyzed either as discrete categories or as continuous phenotypes, depending on the definition of cut-off points, or on the ''metric'' used to quantify them.<ref name="Anderberg 1973">{{cite book|last1=Anderberg|first1=Michael R.|title=Cluster analysis for applications.|date=1973|publisher=Academic Press|location=New York}}</ref>{{rp|27–69}} Mendel himself had to discuss this matter in his famous paper,<ref name=Mendel>{{cite journal|last1=Mendel|first1=Gregor|title=Versuche über Pflanzen Hybriden|journal=Verhandlungen Naturforschender Verein in Brünn|date=1866|volume=iv}}</ref> especially with respect to his peas' attribute ''tall/dwarf'', which actually was derived by adding a cut-off point to "length of stem".<ref name="Mendel Bateson">{{cite journal|last1=Mendel|first1=Gregor |translator-last=Bateson |translator-first=William |title=Experiments in plant hybridisation|journal=J. Roy. Hort. Soc. (London)|date=1891|volume=XXV|pages=54–78}}</ref><ref>The Mendel G.; Bateson W. (1891) paper, with additional comments by Bateson, is reprinted in: Sinnott E.W.; Dunn L.C.; Dobzhansky T. (1958). "Principles of genetics"; New York, McGraw-Hill: 419-443. Footnote 3, page 422 identifies Bateson as the original translator, and provides the reference for that translation.</ref> Analysis of [[Quantitative trait locus|quantitative trait loci]], or QTLs,<ref>A ''QTL'' is a region in the DNA genome that effects, or is associated with, quantitative phenotypic traits.</ref><ref name="W&G&W&Z 1998">{{cite book|last1=Watson|first1=James D.|last2=Gilman|first2=Michael|last3=Witkowski|first3=Jan|last4=Zoller|first4=Mark|title=Recombinant DNA|date=1998|publisher=W.H. Freeman (Scientific American Books)|location=New York|isbn=978-0-7167-1994-6|edition=Second (7th printing)|url=https://archive.org/details/recombinantdna00jame}}</ref><ref name="J&K 2004">{{cite book |editor-last1=Jain |editor-first1=H. K. |editor-last2=Kharkwal |editor-first2=M. C. |title=Plant Breeding - Mendelian to molecular approaches|date=2004|publisher=Kluwer Academic Publishers|location=Boston Dordecht London|isbn=978-1-4020-1981-4}}</ref> is a more recent addition to quantitative genetics, linking it more directly to [[molecular genetics]].