title: Copy Number Variation in TAS2R Bitter Taste Receptor Genes: Structure, Origin, and Population Genetics.
abstract: Bitter taste receptor genes (TAS2Rs) harbor extensive diversity, which is broadly distributed across human populations and strongly associated with taste response phenotypes. The majority of TAS2R variation is composed of single-nucleotide polymorphisms. However, 2 closely positioned loci at 12p13, TAS2R43 and -45, harbor high-frequency deletion (Δ) alleles in which genomic segments are absent, resulting in copy number variation (CNV). To resolve their chromosomal structure and organization, we generated maps using long-range contig alignments and local sequencing across the TAS2R43-45 region. These revealed that the deletion alleles (43Δ and 45Δ) are 37.8 and 32.2kb in length, respectively and span the complete coding region of each gene (~1kb) along with extensive up- and downstream flanking sequence, producing separate CNVs at the 2 loci. Comparisons with a chimpanzee genome, which contained intact homologs of TAS2R43, -45, and nearby TAS2Rs, indicated that the deletions evolved recently, through unequal recombination in a cluster of closely related loci. Population genetic analyses in 946 subjects from 52 worldwide populations revealed that copy number ranged from 0 to 2 at both TAS2R43 and TAS2R45, with 43Δ and 45Δ occurring at high global frequencies (0.33 and 0.18). Estimated recombination rates between the loci were low (ρ = 2.7×10(-4); r = 6.6×10(-9)) and linkage disequilibrium was high (D' = 1.0), consistent with their adjacent genomic positioning and recent origin. Geographic variation pointed to an African origin for the deletions. However, no signatures of natural selection were found in population structure or integrated haplotype scores spanning the region, suggesting that patterns of diversity at TAS2R43 and -45 are primarily due to genetic drift.
authors.affiliation: Department of Molecular Genetics, German Institute of Human Nutrition Potsdam-Rehbruecke, Arthur-Scheunert-Allee 114-116, 14558 Nuthetal, Germany.
authors.forename: Natacha
authors.initials: N
authors.lastname: Roudnitzky
authors.affiliation: National Institute on Deafness and Other Communication Disorders, National Institutes of Health, Bethesda, MD 20892, USA and.
authors.forename: Davide
authors.initials: D
authors.lastname: Risso
authors.affiliation: National Institute on Deafness and Other Communication Disorders, National Institutes of Health, Bethesda, MD 20892, USA and.
authors.forename: Dennis
authors.initials: D
authors.lastname: Drayna
authors.affiliation: Department of Molecular Genetics, German Institute of Human Nutrition Potsdam-Rehbruecke, Arthur-Scheunert-Allee 114-116, 14558 Nuthetal, Germany.
authors.forename: Maik
authors.initials: M
authors.lastname: Behrens
authors.affiliation: Department of Molecular Genetics, German Institute of Human Nutrition Potsdam-Rehbruecke, Arthur-Scheunert-Allee 114-116, 14558 Nuthetal, Germany.
authors.forename: Wolfgang
authors.initials: W
authors.lastname: Meyerhof
authors.affiliation: Health Sciences Research Institute, University of California, Merced, 5200 North Lake Road, Merced, CA 95343, USA swooding@ucmerced.edu.
authors.forename: Stephen P
authors.initials: SP
authors.lastname: Wooding
mesh_terms: D000483:Alleles; D000595:Amino Acid Sequence; D056915:DNA Copy Number Variations / Q000235:genetics*; D005828:Genetics, Population; D006801:Humans; D043562:Receptors, G-Protein-Coupled / Q000235:genetics*; D016415:Sequence Alignment; D013649:Taste / Q000235:genetics; D055697:Taste Perception / Q000235:genetics; D000098706:Taste Receptors, Type 2
chemical_list: D043562:Receptors, G-Protein-Coupled; D000098706:Taste Receptors, Type 2
keywords: bitter; evolution; genetic; genomic; natural selection; taste receptor