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 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 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 in his classic book Evolution by Gene Duplication (1970).[1]