Evolution of sensory receptor genes in humans
Genomic drift and copy number variation of sensory receptor genes in
humans
Masafumi Nozawa*,, Yoshihiro Kawahara*,, and Masatoshi Nei*
"
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 800 OR gene loci in humans were polymorphic
with respect to copy number, and two randomly chosen individuals
showed a copy number difference of 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.
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