A test of the ability to taste the chemical PTC has been a staple of introductory genetics labs for decades. Some people can taste PTC; others are unable to taste it. Although PTC is not found naturally, the ability to taste it is correlated with the ability to taste many naturally occurring bitter compounds (often toxins). In addition, among tasters, there are differences in sensitivity to PTC. Recent studies have shown that most of the variability in PTC perception is correlated with specific combinations of sequence changes in a single gene, hTAS2R38, which encodes a bitter taste receptor.
We will extend the classic taste test by having students sequence their own hTAS2R38 locus and compare the students' specific combination of variations (called a haplotype) with their ability to taste PTC. In addition to studying the genetics of the locus (is the student homozygous or heterozygous for a variant? what are the frequencies of taster versus non-taster haplotypes?), we will consider how changes in the structure of the receptor may give rise to differences in the ability to taste PTC.
PCR and DNA Sequencing
RIBS students will begin the project by determining their sensitivity to PTC or other bitter compounds. They will then extract DNA from their own cheek cells and use the polymerase chain reaction (PCR) to amplify a segment of their PTC (hTAS2R38) taste receptor. We will submit the DNA for sequencing at the UCCRC cancer center sequencing facility on campus. Upon receipt of the sequence, we will use analysis software to identify the sequence changes and we will compare PTC receptor haplotypes to the taste test results. Does genotype predict phenotype?