Taste & genetics

The Associated Press has an article on the genetics of taste and its relevance in everyday life. I've posted on the genetics of taste in the past, it's an interesting topic. Basically, you have three phenotypes:

1. Super-taster
2. Taster
3. Non-taster

Until recently the "super-taster" category was unknown, the crude assays (e.g., tasting PTC doped paper) only distinguished between tasters and non-tasters. The inheritance pattern would have suggested a recessive pattern for the non-tasters, but the super-taster category suggests that we are simply seeing a more additive process where two "on" alleles results in greater sensitivity. Outside of Africa there are only two alleles, and their deep time coexistence suggests that neither is being driven by positive selection to extinguish the other. Here's a recent paper on the topic:

The ability or inability to taste the compound phenylthiocarbamide (PTC) is a classic inherited trait in humans and has been the subject of genetic and anthropological studies for over 70 years. This trait has also been shown to correlate with a number of dietary preferences and thus may have important implications for human health. The recent identification of the gene that underlies this phenotype has produced several surprising findings. This gene is a member of the T2R family of bitter taste receptor genes. It exists in seven different allelic forms, although only two of these, designated the major taster and major non-taster forms, exist at high frequency outside sub-Saharan Africa. The non-taster allele resides on a small chromosomal region identical by descent, indicating that non-tasters are descended from an ancient founder individual, and consistent with an origin of the non-taster allele preceding the emergence of modern humans out of Africa. The two major forms differ from each other at three amino acid positions, and both alleles have been maintained at high frequency by balancing natural selection, suggesting that the non-taster allele serves some function. We hypothesize that this function is to serve as a receptor for another, as yet unidentified toxic bitter substance. At least some of the remaining five haplotypes appear to confer intermediate sensitivity to PTC, suggesting future detailed studies of the relationships between receptor structure and taste function.