Gene Duplication

Gene duplication is a process in which a segment of DNA containing a gene is copied, so that the genome ends up with two or more copies. It is a main source of new genes, because one copy can keep the old function while another is free to change.

Unequal crossing over in meiosis can leave one chromosome with an extra copy of a region. Transposable elements and retrotransposition can copy the RNA of a gene back into DNA, and whole-genome duplication, a form of polyploidy, copies every gene at once. Many plants and some vertebrate lineages have gone through such events.

Most often one copy accumulates mutations and becomes a nonfunctional pseudogene. Sometimes both copies are kept because the extra dosage is useful. In neofunctionalization a copy gains a new function, and in subfunctionalization the copies split the roles of the original. Susumu Ohno's 1970 book Evolution by Gene Duplication argued that this was the main route to new genes.

The globin family, which includes the hemoglobin alpha and beta chains and myoglobin, arose from repeated duplications of a single ancestral gene. Humans have varying numbers of copies of the amylase gene, linked to the starch content of traditional diets, and duplicated opsin genes allow color vision. Gene families are found throughout the genome, and duplication is a key topic in evolution.

• Polyploidy — duplication of whole genomes
• Hemoglobin — a protein family shaped by duplication
• Genome — where duplicated genes are found