This case study introduces concepts within pharmacogenomics and population genetics folded into a story focused on genetic ancestry and how it is distinct from an individual’s racial or ethnic identity. The storyline follows “Dr. Carter,” a neurologist who sees a patient with chronic migraine headaches. Dr. Carter contemplates giving her patient a newly approved medication but notices there is a dosage difference recommended for patients based on their race or ethnicity. In researching gene variants associated with drug metabolism, Dr. Carter discovers differences in allele frequencies based on genetic ancestry. Ultimately, Dr. Carter decides to use genetic testing to determine her patient’s genotype instead of relying on reported race to prescribe the appropriate medication dose. Precision medicine relies on genetic information to inform disease prevention and treatment, and this case illustrates that precision over presumption is a more accurate approach. Designed for introductory-level students, the case could be used in high school classes as well as undergraduate introductory biology, genetics, and human biology courses.