Gene cluster
A gene cluster is a set of two or more genes that serve to encode for the same or similar products. Because populations from a common ancestor tend to possess the same varieties of gene clusters, they are useful for tracing back recent evolutionary history. Because of this, they were used by Luigi Luca Cavalli-Sforza
Luigi Luca Cavalli-Sforza
Luigi Luca Cavalli-Sforza is an Italian population geneticist born in Genoa, who has been a professor at Stanford University since 1970 .-Books:...

 to identify ethnic groups within Homo sapiens and their closeness to each other.

An example of a gene cluster is the Human β-globin gene cluster, which contains five functional genes and one non-functional gene which code for similar proteins. Hemoglobin molecules contain any two identical proteins from this gene cluster, depending on their specific role.

Gene clusters are created by the process of gene duplication
Gene duplication
Gene duplication is any duplication of a region of DNA that contains a gene; it may occur as an error in homologous recombination, a retrotransposition event, or duplication of an entire chromosome.The second copy of the gene is often free from selective pressure — that is, mutations of it have no...

 and divergence
. A gene is accidentally duplicated during cell division, so that its descendants have two copies of the gene, which initially code for the same protein or otherwise have the same function. In the course of subsequent evolution, they diverge, so that the products they code for have different but related functions, with the genes still being adjacent on the chromosome. This may happen repeatedly. The process was described by Susumu Ohno
Susumu Ohno
was an Asian American geneticist and evolutionary biologist, and seminal researcher in the field of molecular evolution.- Biography :Susumu Ohno was born of Japanese parents in Seoul, Korea, on February 1, 1928. The second of five children, he was the son of the minister of education of the...

in his classic book Evolution by Gene Duplication (1970).
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