What is Gene family?
A '''gene family''' is a set of several similar [[genes]]. They occur by the [[gene duplication|duplication]] of a single original gene. Usually they have similar [[biochemical]] [[Function (biology)|function]]s. The idea that genes get duplicated is almost as old as the science of [[genetics]].<ref>Taylor, John S. & Raes, Jeroen 2004. Duplication and divergence: the evolution of new genes and old ideas. ''Annual Review of Genetics'' '''38''': 615-643. [http://www.annualreviews.org/doi/abs/10.1146/annurev.genet.38.072902.092831] {{Webarchive|url=https://web.archive.org/web/20160525105242/http://www.annualreviews.org/doi/abs/10.1146/annurev.genet.38.072902.092831 |date=2016-05-25 }}</ref> One such family are the genes for human [[haemoglobin]] subunits. The ten genes are in two clusters on different [[chromosomes]], called the [[Human α-globin locus|α-globin]] and [[Human β-globin locus|β-globin]] [[loci]]. These two gene clusters are thought to have arisen from a precursor gene being duplicated, about 500 [[million]] years ago.<ref>{{Cite book|title = Thompson & Thompson Genetics in Medicine|last1 = Nussbaum|first1 = Robert L.|publisher = Elsevier|year = 2016|isbn = 978-1-4377-0696-3|location = Philadelphia, PA|pages = 25|last2 = McInnes|first2 = Roderick R.|last3 = Willard|first3 = Huntington F.|edition = 8th}}</ref> The biggest gene family is said to be the [[olfaction]] genes.<ref>Niimura Y. & Nei M. 2003. Evolution of olfactory receptor genes in the human genome. ''Proceedings of the National Academy of Sciences of the United States of America'' '''100''' (21): 12235–40. [http://www.pnas.org/content/100/21/12235] {{Webarchive|url=https://web.archive.org/web/20170315034350/http://www.pnas.org/content/100/21/12235 |date=2017-03-15 }}</ref> The [[homeobox]] genes are another important group.<ref> Bürglin T.R. Affolter M. 2015. Homeodomain proteins: an update. ''Chromosoma'', 1–25. [https://link.springer.com/article/10.1007%2Fs00412-015-0543-8]</ref> Genes for the [[immune system]] include several gene fa