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Tasting Phenylthiocarbamide (PTC): A New Integrative Genetics Lab with an Old Flavor
This article describes an integrative genetics laboratory investigation of phenylthiocarbamide (PTC) taste sensitivity—one of the most widely studied of all human genetic traits. To complete this inquiry and investigative activity, students must draw on their knowledge of Mendelian genetics, population genetics, probability, pedigree analysis, and molecular techniques. Using PTC taste papers, students first determine their individual phenotypes and then calculate the frequencies of the taster and nontaster alleles in the class. These allele frequencies are then used to calculate the probability that tasters are either homozygotes or heterozygotes. Students next use cleaved amplified polymorphic sequence (CAPS) analysis to determine actual student genotypes for the PTC gene, located on the long arm of chromosome 7—a gene whose sequence is primarily responsible for variation in the ability to taste PTC. Students extract cheek cell DNA and use polymerase chain reaction (PCR), followed by a restriction digest and electrophoretic separation of the digestion products, to determine the PTC genotype of each student. The article provides step-by-step protocols for the analysis. It also explains how teachers can use a manual PCR set-up with kitchen appliances to amplify buccal swab DNA—a time-consuming but inexpensive technique. The article contains citations that reference the primary literature on the PTC gene. It ends with a brief discussion of the toxicity of PTC taste papers, with the authors concluding that teachers have no reason to be concerned about the papers’ toxicity. This article was first published in the May 2008 online issue of The American Biology Teacher.
Program Director: Thomas S. Litwin, Ph.D.
Award Years: 1988, 1993, 1996, 2000, 2004, 2008
Summary: Smith College is a private baccalaureate institution in Northampton, Massachusetts. Its HHMI-funded initiatives include:
- Major changes in science curricula, leading to a curriculum-wide adoption of experiential learning pedagogies;
- A Center for the Molecular Biosciences to provide centralized resources for interdisciplinary teaching and research;
- Expanded programs for middle and high school girls and teachers, including the Summer Science and Engineering Program and an Institute for Educators, emphasizing adolescent girls’ health and curricular resources;
- A summer student research fellows program, with an emphasis on the molecular biosciences;
- A major project to assess the outcomes for Smith students participating in the summer student research fellows program from 1967 through 2006; and
- An annual Five College student research symposium in the molecular biosciences.