We have performed a comprehensive evaluation of single-nucleotide polymorphisms (SNPs) and haplotypes in the human TAS1R gene family,which encodes receptors for sweet and umami tastes.Complete DNA sequences of TAS1R1-,TAS1R2-,and TAS1R3-coding regions,obtained from 88 individuals of African,Asian,European,and Native American origin,revealed substantial coding and noncoding diversity: polymorphisms are common in these genes,and polymorphic sites and SNP frequencies vary widely in human populations.The genes TAS1R1 and TAS1R3,which encode proteins that act as a dimer to form the umami (glutamate) taste receptor,showed less variation than the TAS1R2 gene,which acts as a dimer with TAS1R3 to form the sweet taste receptor.The TAS1R3 gene,which encodes a subunit common to both the sweet and umami receptors,was the most conserved.Evolutionary genetic analysis indicates that these variants have come to their current frequencies under natural selection during population growth and support the view that the coding sequence variants affect receptor function.We propose that human populations likely vary little with respect to umami perception,which is controlled by one major form of the receptor that is optimized for detecting glutamate but may vary much more with respect to sweet perception.
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