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 deleterious effects to its host organism. Thus it mutates faster than a functional single-copy gene, over generations of organisms.
Gene duplication is believed to play a major role in evolution; this stance has been held by members of the scientific community for over 100 years. Susumu Ohno was one of the most famous developers of this theory in his classic book Evolution by gene duplication (1970). Some have argued that gene duplication is the most important evolutionary force since the emergence of the universal common ancestor.
Major genome duplication events are not uncommon. It is believed that the entire yeast genome underwent duplication about 100 million years ago. Plants are the most prolific genome duplicators. For example, wheat is hexaploid (a kind of polyploid), meaning that it has six duplicate copies of its genome.
The two genes that exist after a gene duplication event are called paralogs and usually code for proteins with a different function and/or structure. By contrast, orthologous genes are ones which code for proteins with similar functions but exist in different species, and are created from a speciation event. (See Homology of sequences in genetics).
It is important (but often difficult) to differentiate between paralogs and orthologs in biological research. Experiments on human gene function can often be carried out on other species if a homolog to a human gene can be found in the genome of that species, but only if the homolog is orthologous. If they are paralogs and resulted from a gene duplication event, their functions are likely to be too different.
- Zhang, J. (2003). "Evolution by gene duplication: an update." Trends in Ecology & Evolution 18(6): 292-298. DOI link
- Taylor, JS. & Raes, J. (2004). "Duplication and Divergence: The Evolution of New Genes and Old Ideas" Annual Review of Genetics 9: 615-643. DOI link
- Ohno, S. (1970). Evolution by gene duplication. Springer-Verlag. ISBN 0-04-575015-7.
- Kellis, M, Birren, BW & Lander, ES. (2004). "Proof and evolutionary analysis of ancient genome duplication in the yeast Saccharomyces cerevisiae" Nature 428: 617-624.