CHARLOTTE — Twelve students in Charlotte Catholic High School’s Advanced Placement Biology class recently spent a day at Clemson University to study the genetics of bitter taste.
The students and their teacher, Gwenn Freeman, were quite excited to conduct an experiment of this magnitude, using laboratory equipment not available to most high school students.
The students were asked to study the PTC gene, an inherited trait which determines whether people taste phenylthiocarbamide, or PTC, as extremely bitter, slightly bitter or not bitter at all. During the 1930s, geneticists determined that there is an inherited component that influences how a person tastes PTC. In 2003 geneticists discovered that the ability to taste PTC is conveyed by a single gene that codes for a taste receptor on the tongue.
PTC is not found in nature, but the ability to taste it is strongly related to the ability to taste other bitter substances in nature – many of which are poisonous. The ability to taste bitter substances evolved as a way to prevent early humans from eating toxic plants.
Students began their study with a simple test in which they tasted paper containing PTC. Most of the students tasted the PTC as slightly bitter, while a few did not taste it at all, and one tasted it as extremely bitter.
Next, the students took samples of their own DNA, amplified a small segment of each sample approximately 500 billion times using a Polymerase Chain Reaction, and prepared it with the addition of primers and a hot/cold protocol. Last, students used DNA gel electrophoresis to see whether they inherited a dominant gene, a recessive gene or a combination of the two genes from their parents.
“It was a terrific learning experience,” Freeman said. “We enjoyed fantastic instruction from the lab instructor at Clemson, and even had time to enjoy lunch at a new cafeteria and take a brief stroll across campus.”
— Carolyn Kramer Tillman, Special to the Catholic News Herald