duplication of a gene sequence within a genome From Wikipedia, the free encyclopedia
Gene duplication (or gene amplification) is any duplication of a region of DNA that contains a gene.
Gene duplication is important in supplying raw genetic material – new genes – to biological evolution. This has been recognized since the 1930s. Recent genomic sequence data show that duplicated genes are common in all organisms surveyed.[1]
In classical genetics it may occur as an error in crossing-over during meiosis, or the duplication of an entire chromosome.[1]
In non-classical genetics it may happen by a retrotransposition event.[1]
The second copy of the gene is often relatively free from selective pressure. Mutations of it have no deleterious effects to its host organism. Thus it accumulates mutations faster than a functional single-copy gene, over generations.
A duplication is the opposite of a deletion. Duplications arise from unequal crossing-over that occurs during meiosis between misaligned homologous chromosomes. The product of this recombination are a duplication at the site of the exchange and a reciprocal deletion.[2]
Gene duplication is believed to play a major role in evolution; this idea was first suggested 100 years ago.[3] Susumu Ohno was one of the most famous developers of this theory in his classic book Evolution by gene duplication (1970).[4] Ohno argued that gene duplication is the most important evolutionary force since the emergence of the last universal common ancestor (LUCA).[5]
Major genome duplication events are not uncommon. It is believed that the entire yeast genome underwent duplication about 100 million years ago.[6] Plants are the most prolific genome duplicators. For example, wheat is hexaploid (a kind of polyploid), meaning that it has six copies of its genome.
Normally, a big change in gene function is resisted because the original function is needed, but after a duplication one gene carries on the original function. Therefore, a change of function in the second copy is possible without loss of fitness.[7][8][9] This freedom from consequences allows for more mutations to be 'carried' in the population. Some of these might increase the fitness of the organism or code for a new function.
The two genes that exist after a gene duplication event are called paralogs and usually code for proteins with a similar 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 species-splitting.
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