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Neofunctionalization
Neofunctionalization, one of the possible outcomes of functional divergence, occurs when one gene copy, or paralog, takes on a totally new function after a gene duplication event. Neofunctionalization is an adaptive mutation process; meaning one of the gene copies must mutate to develop a function that was not present in the ancestral gene.〔S. Rastogi and D. A. Liberles, “Subfunctionalization of duplicated genes as a transition state to neofunctionalization,” BMC Evolutionary Biology, vol. 5, no. 1, p. 28, 2005〕〔B. Conrad and S. E. Antonarakis, “Gene duplication: a drive for phenotypic diversity and cause of human disease.,” Annual review of genomics and human genetics, vol. 8, pp. 17-35, Jan. 2007〕 In other words, one of the duplicates retains its original function, while the other accumulates molecular changes such that, in time, it can perform a different task.〔S. Ohno, Evolution by Gene Duplication. New York, Heidelberg, Berlin: Springer-Verlag, 1970, pp. 59-87〕 This process is thought to be free of selective pressure because one gene copy can mutate without adversely affecting the fitness of the organism since ancestral function is retained in the other copy.〔M. Sémon and K. H. Wolfe, “Preferential subfunctionalization of slow-evolving genes after allopolyploidization in Xenopus laevis.,” Proceedings of the National Academy of Sciences of the United States of America, vol. 105, no. 24, pp. 8333-8, Jun. 2008〕〔R. De Smet and Y. Van de Peer, “Redundancy and rewiring of genetic networks following genome-wide duplication events.,” Current opinion in plant biology, pp. 1-9, Feb. 2012〕〔J. G. Ruby, A. Stark, W. K. Johnston, M. Kellis, D. P. Bartel, and E. C. Lai, “Evolution, biogenesis, expression, and target predictions of a substantially expanded set of Drosophila microRNAs.,” Genome research, vol. 17, no. 12, pp. 1850-64, Dec. 2007〕〔D. (University of H. Graur and W.-H. (University of C. Li, Fundamentals of Molecular Evolution, Second. Sinauer Associates, Inc.,, 2000〕
==The process==
The process of Neofunctionalization begins with a gene duplication event, which is thought to occur as a defense mechanism against the accumulation of deleterious mutations.〔〔〔G. D. Amoutzias, Y. He, J. Gordon, D. Mossialos, S. G. Oliver, and Y. Van de Peer, “Posttranslational regulation impacts the fate of duplicated genes.,” Proceedings of the National Academy of Sciences of the United States of America, vol. 107, no. 7, pp. 2967-71, Feb. 2010〕 Following the gene duplication event there are two identical copies of the ancestral gene performing exactly the same function. This redundancy allows one the copies to take on a new function. In the event that the new function is advantageous, natural selection positively selects for it and the new mutation becomes fixed in the population.〔〔H. Innan, “Population genetic models of duplicated genes.,” Genetica, vol. 137, no. 1, pp. 19-37, Sep. 2009〕
The occurrence of Neofunctionalization can most often be attributed to changes in the coding region or changes in the regulatory elements of a gene.〔 It is much more rare to see major changes in protein function, such as subunit structure or substrate and ligand affinity, as a result of Neofunctionalization.〔
抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』
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