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J Microbiol Biol Educ. 2013 Dec 2;14(2):197-205. doi: 10.1128/jmbe.v14i2.560. eCollection 2013.

What's Downstream? A Set of Classroom Exercises to Help Students Understand Recessive Epistasis.

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Department of Molecular, Cellular and Developmental Biology, University of Colorado, Boulder, CO 80309-0347.
School of Biology and Ecology, Maine Center for Research in STEM Education (RiSE), University of Maine, Orono, ME 04469.


Undergraduate students in genetics and developmental biology courses often struggle with the concept of epistasis because they are unaware that the logic of gene interactions differs between enzymatic pathways and signaling pathways. If students try to develop and memorize a single simple rule for predicting epistatic relationships without taking into account the nature of the pathway under consideration, they can become confused by cases where the rule does not apply. To remedy this problem, we developed a short pre-/post-test, an in-class activity for small groups, and a series of clicker questions about recessive epistasis in the context of a signaling pathway that intersects with an enzymatic pathway. We also developed a series of homework problems that provide deliberate practice in applying concepts in epistasis to different pathways and experimental situations. Students show significant improvement from pretest to posttest, and perform well on homework and exam questions following this activity. Here we describe these materials, as well as the formative and summative assessment results from one group of students to show how the activities impact student learning.

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