Question No.  19866 :
I have heard that having students use the well-known PTC paper taste test as a genetics lab is dangerous because it can be harmful to students. Is this true? Can you tell me something about the toxicity of PTC? Do you recommend I discontinue using this lab?

In 1931 Arthur L. Fox was synthesizing a compound called phenylthiocarbamide (PTC), when some of it blew into the air. A colleague who inhaled the PTC dust commented on the terrible bitter taste; however, Fox tasted nothing. This sparked early research by Fox on PTC tasting test. PTC is also called phenylthiourea (C6H5NHCSNH2). It is a crystalline compound that tastes intensely bitter to people with a specific dominant gene and is used to test for the presence of the gene. PTC tasting is one of the most frequently administered genetic tests in human populations. The ability to taste PTC is present in about 70% of the overall human population, varying from 58% for Australoid peoples to 98% for Native American populations. Why this trait has been maintained in the population is uncertain but this polymorphism may influence food selection, nutritional status or thyroid metabolism. One study has found that non-smokers and those not habituated to coffee or tea have a statistical higher percentage of tasters than the general population. There is conflicting evidence whether a higher percentage of women taste PTC versus men. The ability to taste the bitter compound PTC and related chemicals is bimodal, and all human populations tested to date contain some people who can and some people who cannot taste PTC. Genome-wide linkage analysis identified a region on chromosome 7q that contains over a hundred genes. Analysis of linkage disequilibrium and single nucleotide polymorphisms (SNPs) narrowed the search to a 30 kb interval containing only a new TAS2R bitter taste receptor gene. The PTC receptor encodes a novel member of the G protein-coupled TAS2R bitter taste receptor family. Three coding SNPs in this gene were identified as giving rise to five haplotypes that accounted for the bimodal distribution of PTC taste sensitivity worldwide. Distinct phenotypes are associated with distinct genotypes and SNPs such as these identifying variations in the PTC receptor would allow taste masking of bitter tasting compounds tailored to the population genetics profile of different groups and populations. Phenylthiocarbamide is very harmful when swallowed, absorbed through the skin or splashed in the eyes. It may be fatal if swallowed or absorbed through the skin. Gloves, protective glasses, and lab coats should be worn when working with this compound. In the 1970's, Linda Bartoshuk began to expand the research of Arthur Fox using a similar chemical called 6-n-propylthiouracil or PROP. Researchers learned that PTC had some toxic effects, so they switch to PROP, a thyroid medication, that has a similar response property as PTC. PROP is a safer chemical that is used in experiment today. Question Asked By:

Name: Steve

Age Group: 30 and above

Occupation Type: Educationalist

Education Level: Others