What is Infinitesimal model?
[[File:LociEffects.png|thumb|447x447px|Normally distributed [[Phenotype|phenotypes]], like [[Trait|traits]] or [[Disease|diseases]], happen because of many [[Gene|genes]] of small effects. If there were only a few genes, the phenotype would not be normally distributed.]] The '''[[infinitesimal]] model''' or '''[[polygenic]] model''' is a way of understanding how [[Trait|traits]] are passed from parents to children using [[Gene|genes]]. It is used a lot in the study of how genes work and in studying all the genes in our DNA. This idea was [[The Correlation between Relatives on the Supposition of Mendelian Inheritance|first shared]] by [[Ronald Fisher]] in 1918. He said that many small genes together can decide how a trait shows up in a person.<ref>{{Cite journal |last1=Nelson |first1=Ronald M. |last2=Pettersson |first2=Mats E. |last3=Carlborg |first3=Örjan |date=December 2013 |title=A century after Fisher: time for a new paradigm in quantitative genetics |journal=Trends in Genetics |volume=29 |issue=12 |pages=669–676 |doi=10.1016/j.tig.2013.09.006 |pmid=24161664 }}</ref> In Fisher's [[The Correlation between Relatives on the Supposition of Mendelian Inheritance|1918 paper]], he explained that if a trait is decided by many genes, then the trait will be [[Normal distribution|normally distributed]] in people.<ref>{{Cite journal |last1=Boyle |first1=Evan A. |last2=Li |first2=Yang I. |last3=Pritchard |first3=Jonathan K. |date=June 2017 |title=An Expanded View of Complex Traits: From Polygenic to Omnigenic |journal=Cell |volume=169 |issue=7 |pages=1177–1186 |doi=10.1016/j.cell.2017.05.038 |pmc=5536862 |pmid=28622505 }}</ref> But it doesn't mean everyone will show the trait in the same way. It depends on their parents' genes.<ref>{{cite journal |last1=Barton |first1=N.H. |last2=Etheridge |first2=A.M. |last3=Véber |first3=A. |title=The infinitesimal model: Definition, derivation, and implications |journal=Theoretical Population Biology |date=December 2017 |volume=118 |pages=50–73 |doi=10.1016/j.tpb.2017.06.001|pmid=2870