Nature Genetics
26, 221 - 224 (2000)
doi:10.1038/79957
Dichotomy of single-nucleotide polymorphism haplotypes in olfactory receptor genes and pseudogenesYoav Gilad1, Daniel Segré1, Karl Skorecki2, Michael W. Nachman3, Doron Lancet1
& Dror Sharon1, 41
Department of Molecular Genetics and the Crown Human Genome Center, The Weizmann Institute of Science, Rehovot, Israel. 2
Molecular Medicine Laboratory and Department of Nephrology, Faculty of Medicine, Technion-Israel Institute of Technology, Bat-Galim, Haifa, Israel. 3
Department of Ecology and Evolutionary Biology, BioSciences West Bldg., University of Arizona, Tucson, Arizona, USA. 4
Present address: Ocular Molecular Genetics Lab, Massachusetts Eye and Ear Infirmary, Harvard Medical School, Boston, Massachusetts, USA.
Correspondence should be addressed to Doron Lancet doron.lancet@weizmann.ac.ilSubstantial efforts are focused on identifying single-nucleotide polymorphisms (SNPs) throughout the human genome, particularly in coding regions (cSNPs), for both linkage disequilibrium and association studies1,
2. Less attention, however, has been directed to the clarification of evolutionary processes that are responsible for the variability in nucleotide diversity among different regions of the genome3. We report here the population sequence diversity of genomic segments within a 450-kb cluster4,
5 of olfactory receptor (OR) genes6,
7 on human chromosome 17. We found a dichotomy in the pattern of nucleotide diversity between OR pseudogenes and introns on the one hand and the closely interspersed intact genes on the other. We suggest that weak positive selection is responsible for the observed patterns of genetic variation. This is inferred from a lower ratio of polymorphism to divergence in genes compared with pseudogenes or introns, high non-synonymous substitution rates in OR genes, and a small but significant overall reduction in variability in the entire OR gene cluster compared with other genomic regions. The dichotomy among functionally different segments within a short genomic distance requires high recombination rates within this OR cluster. Our work demonstrates the impact of weak positive selection on human nucleotide diversity, and has implications for the evolution of the olfactory repertoire.
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