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The Correlation of PTC Tasting Threshold to The TAS2R38 Genotype

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The ability to taste the bitter chemical phenylthiocarbamide (PTC) is an example of dimorphism, a type of polymorphism, with the coexistence of two phenotypes of a character. Most human population are dimorphic, can either detect PTC as a foul, bitter taste or cannot taste it at all. The pedigree in Figure (a) is an example of how two tasters sometimes produce nontaster children.1 According to this pedigree we can conclude that the allele that confers the ability to taste is dominant and that the allele for non tasting is recessive.1

Figure (a): Pedigree for the ability to taste the chemical PTC.

Variation in PTC sensitivity was first discovered in a lab incident in the early 1930s by Arthur L. Fox, an OSHA officer (Fox 1932), when Fox was pouring some PTC powder into a bottle and some “flew around in the air”, a co-worker nearby, C. R. Noller complained that the dust tasted bitter, but Fox insisted he could not taste anything. The two then took turns tasting the PTC powder and found they really differed dramatically in sensitivity. Fox tested “a large number” of people and found a distinct variation was common regardless of age, sex and ethnicity. He classified those people into two categories, those able to taste the PTC at very low concentrations whom he referred to as “tasters” and those unable to taste the PTC except at very high concentrations whom he referred to as “nontasters” or “taste blind”.2 Later several scientists including Fisher, Ford and Huxley (Fisher 1939) and others set out tests for PTC taste sensitivity and the implications of variability of the findings. However, despite almost 70 years of interest, these studies were missing a firm grasp of the molecular genetics of bitter-taste sensitivity.2
When Hoon e...

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