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Beyond Bitterness

If your spouse hates Brussels sprouts and you love them, there may be a straightforward explanation: a gene known as TAS2R38.  Some people have a variant that amplifies their sensitivity to the compound that accounts for that vegetable’s bitterness, and some people don’t. Bitter taste perception has often been explained in evolutionary terms as a dietary adaptation.  Since many toxic substances are bitter, a heightened ability to detect particular bitter compounds could have conferred a survival advantage. 

But in a study of genetic variability among several hundred individuals hailing from 57 distinct populations in Central and East Africa, a team led by Sarah Tishkoff, the David and Lyn Silfen University Associate Professor in the genetics and biology departments [“Proof of Concept, Sept|Oct 2008], discovered something a little surprising: taste is only part of the story, and maybe not the main one.  

After testing the subjects’ ability to taste a bitter compound for which TAS2R38 codes a taste receptor protein, the team found no relationship between that ability and the subjects’ quite disparate traditional diets—suggesting, as postdoctoral researcher Michael Campbell put it, “that variation at this gene serves some other function beyond oral sensory perception.”  The finding appeared in Molecular Biology and Evolution.

Indeed, other studies have found receptors similar to TAS2R38 in the lungs and gut.  “Why are we ‘tasting’ in our guts or in our lungs?” said Tishkoff. “There must be something else that these taste receptors are doing.”

Whatever that is, there’s reason to believe it’s physiologically important, she added.  The data indicate that this gene is millions of years old, predating the evolution of modern humans.

The Altai-America Express

It has long been supposed that the deep ancestors of Native American peoples came from the Eastern Hemisphere.  A team of Penn anthropologists, led by associate professor Theodore Schurr, has used genetic analysis to zero in—with a remarkably high degree of precision—on one place that appears to have harbored some of the earliest Americans’ forebears: the Altai mountains, a region of southern Siberia wedged up against China, Mongolia, and Kazakhstan.  

Schurr and his colleagues, including collaborators from Russia’s Institute of Cytology and Genetics, found a unique mutation on the Y chromosome that is shared by Native Americans and southern Altaians. Additional similarities in the mitochondrial DNA of both groups bolster the likelihood that Native Americans split off from the southern Altaian lineage around 13,000 or 14,000 years ago—about 1,000 years before the human migration across the then-exposed Bering Land Bridge is thought to have occurred.  The study, published in the American Journal of Human Genetics, is not the first to report a genetic link between prehistoric Siberians and Native Americans, but its high-resolution genetic analysis enables a more fine-grained description of this branch of humanity’s phylogenetic tree.

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