This PowerPoint-driven case study provides an applied context for the study of the structure of nucleotides and DNA, the classes and frequencies of single nucleotide mutations, and the process of DNA replication. Students prepare for the case by reading a news article in The New York Times (subscription required) from the early 1990s about the transmission of HIV from a dentist to several of his patients. Students are tasked with the goal of determining if the dentist was likely to have infected so many patients using DNA evidence. The instructor uses a slide deck (see Supplemental Materials) to help students complete a series of questions in the case study handout. After a review of how mutations occur and the likelihood of different types of mutations, students apply their knowledge of DNA replication to PCR and sequencing to copy and then read the sequence of an HIV gene. Using sequence alignment and their new knowledge of HIV-specific mutation rates, students determine how many patients were likely to have been infected by the dentist. The case was originally designed for an upper-level genetics course but could be easily adapted for a more general course focusing on applications of genetics and biotechnology.