Reinventing the Ames Test as a Quantitative Lab That Connects Classical and Molecular Genetics

Abstract

While many institutions use a version of the Ames test in the undergraduate genetics laboratory, students typically are not exposed to techniques or procedures beyond qualitative analysis of phenotypic reversion, thereby seriously limiting the scope of learning. We have extended the Ames test to include both quantitative analysis of reversion frequency and molecular analysis of revertant gene sequences. By giving students a role in designing their quantitative methods and analyses, students practice and apply quantitative skills. To help students connect classical and molecular genetic concepts and techniques, we report here procedures for characterizing the molecular lesions that confer a revertant phenotype. We suggest undertaking reversion of both missense and frameshift mutants to allow a more sophisticated molecular genetic analysis. These modifications and additions broaden the educational content of the traditional Ames test teaching laboratory, while simultaneously enhancing students' skills in experimental design, quantitative analysis, and data interpretation. While data analysis has long been a staple of student learning, recent research demonstrates that students become most engaged and learn best when they have a hand in the design of experiments as well as in the execution and analysis of resulting data (Hake 1998;Merkel 2003;Handelsman et al. 2007). Inquiry-based labs have been shown to improve students' research skills in biology (Myers and Burgess 2003). Further, as suggested by BIO2010 (National Research Council 2003), biology curricula should explicitly build the quantitative skills of budding biologists. Hack and Kendall (2005) argue that biology curricula should change because current life science students must learn to use models, to apply appropriate mathematic tools and statistics to solve problems, and to manage and integrate data. That these tools are best taught in the context of biology courses themselves has been demonstrated by Metz (2008), who has shown that undergraduate biology students do not make connections between quantitative concepts taught in mathematics and statistics courses and their application to biological problems. Metz (2008) demonstrates that inclusion of quantitative and statistical analyses in biology laboratory courses led to significant gains in long-term retention of such knowledge, regardless of whether students also had taken courses in statistics.To address the issue of connecting quantitative analysis and biological problem solving, we have extended the open-ended Ames test for the undergraduate genetics lab to allow students to practice quantitative skills during student-driven experimental design and analysis. Students bring to the lab potential mutagens of their choice, and they are charged both with creating methods to determine the number of colony-forming units (CFUs) per bacterial culture and with using that figure to determine reversion frequencies. We find that this is a difficult task for students, but having them conclude what sort of s...

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