National Institute on Deafness and Other Communication Disorders, NIH, Bethesda, MD 20892, USA.
Department of Biological, Geological and Environmental Sciences BiGeA, Laboratory of Molecular Anthropology and Centre for Genome Biology, University of Bologna, via Selmi 3, 40126 Bologna, Italy.
Sci Rep. 2016 May 3;6:25506. doi: 10.1038/srep25506.
The ability to taste phenylthiocarbamide (PTC) and 6-n-propylthiouracil (PROP) is a polymorphic trait mediated by the TAS2R38 bitter taste receptor gene. It has long been hypothesized that global genetic diversity at this locus evolved under pervasive pressures from balancing natural selection. However, recent high-resolution population genetic studies of TAS2Rs suggest that demographic events have played a critical role in the evolution of these genes. We here utilized the largest TAS2R38 database yet analyzed, consisting of 5,589 individuals from 105 populations, to examine natural selection, haplotype frequencies and linkage disequilibrium to estimate the effects of both selection and demography on contemporary patterns of variation at this locus. We found signs of an ancient balancing selection acting on this gene but no post Out-Of-Africa departures from neutrality, implying that the current observed patterns of variation can be predominantly explained by demographic, rather than selective events. In addition, we found signatures of ancient selective forces acting on different African TAS2R38 haplotypes. Collectively our results provide evidence for a relaxation of recent selective forces acting on this gene and a revised hypothesis for the origins of the present-day worldwide distribution of TAS2R38 haplotypes.
对苯硫脲（PTC）和 6-正丙基硫脲（PROP）的味觉能力是由 TAS2R38 苦味受体基因介导的多态性特征。长期以来，人们一直假设该基因座的全球遗传多样性是在平衡自然选择的普遍压力下进化而来的。然而，最近对 TAS2R 进行的高分辨率群体遗传学研究表明，人口统计学事件在这些基因的进化中发挥了关键作用。我们利用迄今为止分析的最大的 TAS2R38 数据库，该数据库由来自 105 个群体的 5589 个人组成，来研究自然选择、单倍型频率和连锁不平衡，以估计选择和人口统计学对该基因座当代变异模式的影响。我们发现该基因存在古老的平衡选择迹象，但没有离开非洲后的中性偏离，这意味着目前观察到的变异模式主要可以用人口统计学而不是选择性事件来解释。此外，我们还发现了古老的选择压力作用于不同非洲 TAS2R38 单倍型的迹象。总的来说，我们的研究结果为该基因最近的选择压力放松提供了证据，并为 TAS2R38 单倍型当今全球分布的起源提供了一个修正的假说。
