Genomic drift and copy number variation of sensory receptor genes in humans

Abstract

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 Ϸ800 OR gene loci in humans were polymorphic with respect to copy number, and two randomly chosen individuals showed a copy number difference of Ϸ11 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

Targeted resequencing of a genomic region influencing tameness and aggression reveals multiple signals of positive selection

“…Copy number variation in chemosensory receptor genes among humans has been argued to be evolutionarily neutral (Nozawa et al, 2007), raising the possibility that the sequence variants in vomeronasal receptor genes identified here may not be functionally important. However, given the strong influence of the pheromone system on rodent behavior, including aggression (Dulac and Torello, 2003), a tantalizing alternative is that one or several of these variants may influence tameness and aggression.…”

Evolution of F-box genes in plants: Different modes of sequence divergence and their relationships with functional diversification

“…Several recent studies have shown that the variation in gene number does not always result in the difference in fitness (3,6,26). In particular, random genomic drift has been shown to play key roles in the evolution of rapidly-duplicating genes, such as chemosensory receptor genes (27).…”

“…The reason for the great variation in gene number is not always clear. However, several recent studies suggest that the number of genes in a family was initially determined by their functional requirement, but after the number reached a sufficient level, the number can increase or decrease by chance (2,4,6,7).…”

Extraordinary Diversity of Chemosensory Receptor Gene Repertoires Among Vertebrates

“…More recently, the variation of OR gene number was also identified among different human individuals, which is known as the copy number variation (Trask et al 1998 ;Wong et al 2007) . Interestingly, the level of interspecific divergence relative to that of intraspecific variation in OR gene copy number is not significantly different between functional genes and pseudogenes, suggesting that human intraspecific and human-chimpanzee interspecific OR gene number variations may not have any fitness consequence (Nozawa et al 2007 ;Zhang 2007) .…”