Genetic engineering has allowed scientists to express specific genes in foods, creating desired effects such as pesticide and herbicide resistance, increased nutritional value, and stress tolerance. The benefits and risks of consuming genetically modified organisms (GMOs) are hotly debated worldwide. "Detecting Genetically Modified Food by PCR" is a hands-on laboratory investigation designed to bring this topic into the classroom. Students use the kit to test corn- or soy-containing food products of their choice for the presence of genetic modification. Wild-type and Round-Up Ready soybeans are provided in the kit and used as controls. The methodology used includes DNA extraction, PCR, gel electrophoresis, and bioinformatics analysis. Given the technical nature of the investigation, the kit is most appropriate for use in high school or college courses.
Learning Goals & Standards
The material in the kit was designed by the DNA Learning Center, an organization that provides educational programs and resources for biology (http://www.dnalc.org). The concepts addressed by the kit, such as "the relationship between genotype and phenotype," are clearly stated in the manual. The kit is definitely designed for educators, as it contains background information, student assessment questions, extension activities, and a CD containing handouts, animations, and other resources.
Materials & Preparations
Each kit has enough materials to process up to 10 food samples plus the 2 soy plant controls (24 PCR reactions total). The soybean seeds included in the kit must be planted 2–3 weeks prior to the start of the experiment in order to harvest the leaves. A few days before the experiment, students must research and then purchase the food product they wish to test. Only a small amount of food is required, such as one chip or a few pieces of cereal. Other items required include a thermal cycler, gel electrophoresis equipment, and micropipets and tips. The manual includes an instructor checklist and approximate completion times for each part of the experiment to assist with scheduling.
The best part of using this kit is the ease with which students get to conduct actual research. When I have used this kit in my introductory college biology course, we first decide as a class which category of food product to investigate. Categories that have worked successfully in my class include snack foods, cereals, and even fitness/power bars. To get students interested in the experiment, it is important to allow them to test a food brand that they commonly consume. By testing only one category of food, data from the entire class can be pooled to compare different brands in that category for genetic modification.
The protocol for students is clear and includes a visual flow chart of each stage. The first stage involves extracting DNA from the foods and controls. The kit calls for each student group to isolate DNA from one of the controls. However, my suggestion is that the instructor extracts DNA from the two controls and allows students to work only on their foods. Next, each DNA sample is used in two separate PCR reactions. One reaction uses primers for tubulin, a gene expressed in all plants, to provide evidence of amplifiable DNA in the extraction. The second primer set amplifies the 35S promoter, a common promoter used in plants to drive expression of a transgene. The presence of a 35S PCR product is diagnostic for genetic modification. Finally, the PCR reactions are analyzed using gel electrophoresis and staining. The above sequence of stages allows for flexibility in scheduling because the results of the DNA extraction and the PCR reactions can both be stored in a freezer before proceeding to the next stage.
The kit also provides directions for an activity on bioinformatics. Using the primer sequences provided in the manual, Basic Local Alignment Search Tool (BLAST) can be used to determine the sequences of the portion of the 35S promoter and the tubulin gene amplified by PCR. One extension activity that I often use is to have students troubleshoot any results that are inconclusive. Given the variety of foods available for testing, it is not surprising that some may contain natural inhibitors of the DNA extraction or PCR stages. Students research and compile lists of known inhibitors and then compare that list to the ingredients in the food. If possible, students then propose a modification to the protocol to troubleshoot the issue. The results of the food analysis can also be used to launch a discussion on GMO labeling policies. Students can research labeling policies in other countries and then debate the pros and cons of instituting a GMO labeling policy in the United States. As an extension to the discussion, students work in groups to design potential labels for food products that were identified as genetically modified in the experiment. When given the ability to be creative and use their minds for critical analysis, it is simply amazing the quality of learning that students can achieve.
Overall, "Detecting Genetically Modified Food by PCR" is an excellent student-inquiry based experience. The kit was easy to use, modifiable, extendable, and allowed students to experience novel research instead of a typical cookbook experiment. Students were able to learn and experience some of the techniques used by molecular biologists, including DNA extraction, PCR, gel electrophoresis, and bioinformatics. Most importantly, the kit provided the launching point for discussion and reflection by my students on the impacts of GMOs in their lives.