Evolution of Bitter Taste Receptors
Of the five basic tastes, three (sweet, bitter and umami tastes) are mediated by receptors from the G protein-coupled receptor family. Mammalian bitter taste receptors (T2Rs) are encoded by a gene family of only a few dozen members. It is believed that bitter taste receptors evolved as a mechanism to avoid ingesting poisonous and harmful substances. If this is the case, one might expect different species to develop different bitter taste receptors based on dietary and geographical constraints. With the exception of T2R1 (which lies on chromosome 5) all human bitter taste receptor genes can be found clustered on chromosome 7 and chromosome 12. Analyzing the relationships between bitter taste receptor genes show that the genes on the same chromosome are more closely related to each other than genes on different chromosomes. Furthermore, the genes on chromosome 12 have higher sequence similarity than the genes found on chromosome 7. This indicated that these genes evolved via tandem gene duplications and that chromosome 12, as a result of its higher sequence similarity between its genes, went through these tandem duplications more recently than the genes on chromosome 7.
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