A Guest Post from Dr. Rebecca Price: Important Learning Gains from Genetic Drift and Bottlenecked Ferrets

I'm excited to turn my blog over to Rebecca Price from the University of Washington, Bothell. Rebecca investigates how students overcome their conceptual difficulties understanding evolution, and recently collaborated with our research division on a neat study involving one of my favorite SimBio modules. Thanks, Rebecca, for sharing!

-Eli Meir

Do you find that your students are convinced that all evolution happens through natural selection? If so, you are not alone! Genetic drift as another mode of evolution is particularly difficult to convey. The phrase itself, genetic drift, is confusing—students see the word “drift” and think of migration, rather than changes within a population. Or they hear us define genetic drift as random changes, but associate the word random with mutation. Before students can even begin to reconcile genetic drift with other mechanisms of evolution, they first need to straighten out their vocabulary.

To be able to master the vocabulary of evolution, students first need to acknowledge that natural selection is not the only mechanism of evolutionary change (a hard idea, see Price and Perez 2016). They must understand that both mutation and genetic drift involve randomness, and that they are distinct processes. They must be able to distinguish between genetic drift and gene flow, two important evolutionary processes with unfortunately similar names. My colleagues and I document all of these known impediments (and others) in this paper. Given the myriad of challenges, instruction can be even less than inadequate, as I recently found while working in collaboration with folks at SimBio (Price et al. 2016).

We used the Genetic Drift Inventory (or GeDI, may the force be with you, Price et al. 2014) to measure student performance before and after instruction on genetic drift. We found that students understanding of genetic drift can actually decrease during traditional instruction. Traditionally-taught students performed slightly better after instruction on the questions about misconceptions, but their performance on items about key concepts in genetic drift dropped significantly. It’s a frustrating result for which we do not have a good explanation.

We also had an encouraging result (Price et al. 2016). The Genetic Drift and Bottlenecked Ferrets lab, an interactive tutorial developed by SimBio, does an excellent job at teaching genetic drift. We found that the students in our study who completed this module showed significant learning gains on both misconceptions and key concepts. Keep in mind that the Ferrets module, like all SimBio material, was developed with the best pedagogical practices in mind. Students actively engage with the concepts of genetic drift by observing how allele frequencies change in small populations and in large populations, they try to explain their observations, and they make and test predictions based on those observations. They even get to develop a conservation plan for the ferrets, and then use the simulations to test the efficacy of that plan.

We aren’t exactly sure why we saw this difference between traditional instruction and the SimBio lab, but it could be that introducing drift only briefly and passively, as is typically done, confuses students. The hands-on work in the lab, by contrast, may make the difference in producing great learning gains in a relatively short amount of time. Two hours may be more than most instructors spend on genetic drift, but I think the learning gains are well worth the investment. Moreover, the module can complement what you’ve prepared in lecture; you do not need to spend more class time on genetic drift if the module is assigned as homework.

Prior to playing with ferrets, your students may have shared the common mindset that natural selection is the sole force behind evolution, but after using the Ferrets module, they will understand how and why genetic drift is important as well.

- Dr. Rebecca M. Price; University of Washington, Bothell

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