2New England Biolabs, Ipswich, MA, USA
Both authors are members of BioTechniques’ Editorial Board.
With this article, BioTechniques initiates a bimonthly column (along with expanded online resources) that will focus on amplifying molecular biology experience at the elementary, secondary, and collegiate levels. This column endeavors to offer absorbing, relatively simple experiments that will engage students’ imaginations, along with short commentaries and perspectives. Where possible, we will also present insights on fellow scientists’ involvement with school communities (an enriching experience that we and hundreds of other scientists have already discovered). By dedicating a regular section to educational outreach, we aim to involve readers of BioTechniques in a communal effort to further connect with the next generation of scientists. BioTechniques encourages readers to submit interesting new experiments, or experiments that have been successful in a learning environment, along with suggestions, commentary, or advice.Tasting PTC: A New Lab with an Old Flavor
The following experiment, published by Robert B. Merritt (along with the editors and others), in The American Biology Teacher (1), is suitable for students in middle school, high school, or college. To suit any curriculum, elements can be added to emphasize molecular biology, genetics, population biology, and bioinformatic analysis. It has been tested in several schools, and it was included in the module for the Smith College Summer Science and Engineering Program and the New England Biolabs Molecular Biology Summer Courses.
The basic premise of the exercise is that a simple genetic trait—the ability to taste the non-toxic chemical phenylthiocarbamide (PTC) impregnated on filter paper—provides a model for Mendelian inheritance that students can actually apply to themselves. The PTC taster/nontaster trait is polymorphic, and even small classes will see variations in the ability to taste PTC and in the gene responsible for this ability.
The experiment involves a cheek-cell swab, followed by quick DNA isolation and polymerase chain reaction (PCR) amplification with an oligonucleotide primer pair designed to cross a polymorphic restriction endonuclease site (Fnu4H). In most cases, the presence or absence of this site correlates with inheritance of the trait. A quick restriction endonuclease digestion of the PCR product, followed by agarose gel electrophoresis and visualization of the gel, enables the students to correlate their phenotype (i.e., presence or absence of PTC taste) with their genotype (i.e., presence or absence of the endonuclease site). Furthermore, students can analyze the population biology of the taster phenotype polymorphism (for example, calculate homozygote and heterozygote frequencies using Hardy-Weinberg equilibrium genotypic frequencies), and compare it to the population genotype data they obtain in class. A discussion of the polymorphism's evolutionary history might also spark interest.
The protocol is fast (PCR analysis takes about 3 hours) and costs $1–2 per student. The only major resources needed are a thermal cycler, agarose gel electrophoresis, and detection ability. The complete protocol is accessible online without charge, and even includes an outline of how to make an inexpensive thermal cycler if a commercial model is not available (1). Alternatively, as with many experiments requiring equipment that schools may not have, this experiment provides the opportunity to bring the students into your laboratory to perform either the entire protocol or an individual PCR or electrophoresis step. This circumvents any equipment limitations and also gives the students the opportunity to experience a real working laboratory. Results and discussion could then be presented in the school classroom.