Senior author Sarah Tishkoff, a Penn Integrates Knowledge Professor with appointments in the School of Arts and Sciences' Department of Biology and Penn Medicine's Department of Genetics, said because Africa is the site of origin of all modern humans, Africans are going to have a large amount of diversity and non-Africans are going to have a subset of that diversity.
The work builds on a previous study by the group, which explored the evolutionary history of a gene called TAS2R38, responsible for the ability to perceive the bitter tasting compound PTC.
The current work examines the related gene TAS2R16, which codes for a molecular receptor that binds salicin. Salicin is a chemical found naturally in willow bark, the source of aspirin.
To understand the patterns of variation at TAS2R16 in humans globally, the researchers collected DNA from 595 people in 74 populations across Africa with diverse lifestyles, such as pastoralism, hunting-gathering and agriculture.
They sequenced the stretch of DNA encompassing the TAS2R16 gene in all of these individuals and also examined previously collected DNA from 94 non-Africans from the Middle East, Europe, East Asia and the Americas and found 15 variants total, most of which were only found in Africa.
In addition, the researchers asked 296 of the Africans sampled to perform "taste tests" of progressively more concentrated solutions of salicin and report when they could detect a bitter taste. The team also performed a cellular analysis, led by Integral Molecular scientists, to see the molecular effects of different TAS2R16 mutations.
When the researchers "mapped" individuals' genetic profiles onto their tasting ability, they found a strong correlation between one of the 15 variants and an increased sensitivity to salicin.
The cell-based analysis offered an explanation for this sensitivity: cells with this genetic mutation had nearly twice as many receptors for salicin on their membranes as did cells with other forms of the TAS2R16 gene.
The study has been published in the journal Molecular Biology and Evolution.
--ANI (Posted on 12-11-2013)