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Published online on December 5, 2007, 10.1073/pnas.0709956104
PNAS | December 18, 2007 | vol. 104 | no. 51 | 20421-20426


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From the Cover
BIOLOGICAL SCIENCES / EVOLUTION
Genomic drift and copy number variation of sensory receptor genes in humans

Masafumi Nozawa*,{dagger}, Yoshihiro Kawahara*,{ddagger}, and Masatoshi Nei*

*Institute of Molecular Evolutionary Genetics and Department of Biology, Pennsylvania State University, 328 Mueller Laboratory, University Park, PA 16802; and {ddagger}Integrated Database Team, Japan Biological Information Research Center, 2-42 Aomi, Koto-ku, Tokyo 135-0064, Japan

Contributed by Masatoshi Nei, October 18, 2007 (received for review October 3, 2007)

The number of sensory receptor genes varies extensively among different mammalian species. This variation is believed to be caused partly by physiological requirements of animals and partly by genomic drift due to random duplication and deletion of genes. If the contribution of genomic drift is substantial, each species should contain a significant amount of copy number variation (CNV). We therefore investigated CNVs in sensory receptor genes among 270 healthy humans by using published CNV data. The results indicated that olfactory receptor (OR), taste receptor type 2, and vomeronasal receptor type 1 genes show a high level of intraspecific CNVs. In particular, >30% of the {approx}800 OR gene loci in humans were polymorphic with respect to copy number, and two randomly chosen individuals showed a copy number difference of {approx}11 in functional OR genes on average. There was no significant difference in the amount of CNVs between functional and nonfunctional OR genes. Because pseudogenes are expected to evolve in a neutral fashion, this observation suggests that functional OR genes also have evolved in a similar manner with respect to copy number change. In addition, we found that the evolutionary change of copy number of OR genes approximately follows the Gaussian process in probability theory, and the copy number divergence between populations has increased with evolutionary time. We therefore conclude that genomic drift plays an important role for generating intra- and interspecific CNVs of sensory receptor genes. Similar results were obtained when all annotated genes were analyzed.

birth–death process | copy number evolution | human evolution | multigene family | olfactory receptor

Author contributions: M. Nei and M. Nozawa designed research; M. Nozawa and Y.K. analyzed data; and M. Nei and M. Nozawa wrote the paper.

The authors declare no conflict of interest.

See Commentary on page 20147.

This article contains supporting information online at www.pnas.org/cgi/content/full/0709956104/DC1.

{dagger}To whom correspondence should be addressed. E-mail: mun12{at}psu.edu

© 2007 by The National Academy of Sciences of the USA


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Related Commentary in PNAS:

The drifting human genome
Jianzhi Zhang
PNAS 2007 104: 20147-20148. [Extract] [Full Text]  



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