Abstract
Moving beyond the basic concepts of autosomal Mendelian inheritance to sex-linkage can be difficult for introductory biology students. Although crosses with Drosophila fruit flies have long been a mainstay of genetics units that teach these concepts, they can be unwieldy for large numbers of students, take much of a semester to complete, and require substantial preparation time. We developed a guided exploration laboratory activity that illustrates the contrasts between sex-linked and autosomal inheritance mechanisms in one class period and can be applied easily in multiple sections of a large course. The activity sets up the background information of Thomas Hunt Morgan's famous crossing experiments that demonstrated sex linkage of the white eye color gene in Drosophila and asks students to apply skills learned in the previous autosomal inheritance unit to predict key aspects of his results (i.e., sex and phenotypic ratios of the F2 offspring). They then do a hands-on genetics laboratory activity by anesthetizing and sexing flies before analyzing provided data from Morgan's cross. Students interpret these results, pose an inheritance hypothesis, and revisit their original ratio predictions. Finally, review questions guide students toward recognizing and applying the contrasts between autosomal and sex-linked inheritance. We have tested this activity in over twenty of our own sections, assessed student performance with pre- and post-tests concerning sex-linked inheritance, and surveyed student opinion of the activity. Student response has been positive, both in terms of learning and enthusiasm. Our lesson can be modified and adapted easily to different classroom environments and course contexts.