Activities in class before tidbit: Pre-assessment clicker questions that ask questions about evolution, natural selection, and mutation Discussion of Huntington’s disease (HD) in the Dutch population that migrated to South Africa Activities during tidbit: Students sample from a population of haploid, sexually reproducing organisms, creating a small “founder” population from a larger “source” population Students plot their data Discussion 1: Did everyone get 50:50? Who got more orange? More blue? Anybody have just one color? If we extend this out several generations, what do you think will happen? Discussion 2a: Look at your graph, what happened to the frequency of orange over time? Is this evolution? Discussion 2b: Look around the room – how does your data differ from those collected by other groups? Why might this be? Discussion 2c: Was there selection? Focus on one graph that goes to (or near) fixation Pre-assessments (Outcome 1,2): Responses to the clicker questions will indicate if students grasp the major concept from the previous lecture (natural selection and mutation) Groups develop hypotheses about the high rates of HD in South African immigrants. Responses will provide evidence about their understanding of evolutionary mechanisms Tidbit assessments (Outcome 3,4,5,6,7): Students demonstrate whether they can effectively derive frequencies of a phenotype and accurately plot the data Group responses reflect that students understand that founder populations are not always the same, and are not necessarily reflective of phenotype/allele frequencies in the source population Group responses reflect that students understand that change over time in a founder population is ultimately constrained by the phenotype/allele frequencies of the founder population Group responses reflect that students understand that change over time in different founder populations can be highly variable due to different starting conditions in the founder populations. Group responses reflect that students understand that fixation of a phenotype/allele does not necessarily mean selection is occurring, but rather that it can be a product of Diversity in the tidbit: We will provide verbal and written instructions about the tidbit activity Students work in a group setting. This includes cooperating to complete the activity, as well as talking about the discussion questions in a group as well as with the whole class
Discussion 4: Return to example, tie in results from M&Ms activity, show full graph with incidence of HD in native South Africans. At this point, the term “founder effect” is introduced. Activities after class Homework assignment simulation program Next class: Discussion of homework Next class: Case study: Conservation genetics of Cape buffalo. The concept of a bottleneck is introduced. phenotype/allele loss when a small founder population is established from a larger source population. Students conclude that the incidence of HD in Afrikaners is not adaptive, as there is no increased incidence of this disease in native South Africans. Instead, this is an example of random genetic drift. Post-tidbit assessment (Outcomes 3,4,5,6,7,8): Students can understand how adjusting the parameters of drift (starting population size) and selection (fitness differences between alleles) impact the evolution of population Students conclude that multiple biological scenarios can result in small population sizes that are strongly affected by drift. Students are exposed to the concept of drift through action (collecting data in class, manipulating variables during simulations and writing (summarizing their answers when responding to the homework questions). Reading could also be accommodated by incorporating a post-unit reading of the textbook or a foundational paper, such as Dobzhansky and Pavlovsky (1957) Sample Presentation Plan (detailed schedule with approximate timing for unit) Session 1