This classroom activity is based on a constructivist learning design and engages students in physically constructing a karyotype of three mock patients. Students then diagnose the chromosomal aneuploidy based on the karyotype, list the symptoms associated with the disorder, and discuss the implications of the diagnosis. This activity is targeted at undergraduates in a nonmajors genetics course, but the goals align with AP Biology Big Idea 3 and Next Generation Science Standards HS-LS3. The activity illustrates the relationship between genotype and phenotype, reinforces the chromosome theory of inheritance, and includes mapping of meiotic nondisjunction events.