In December 2023, the Food and Drug Administration (FDA) approved the first gene therapy using CRISPR-Cas9 gene editing to treat sickle cell anemia. This case study covers the basic mechanism of CRISPR-Cas9 gene editing in its original context (the bacterial adaptive immune response) and in the context of medical application of the gene editing tool. Starting with the hemoglobin protein and gene subunits, students learn about a single nucleotide change (SNP) that results in a cascade of consequences from an amino acid change to the overall structure and function of the hemoglobin protein. They then examine the consequences of the SNP in homozygous and heterozygous individuals, applying ideas underlying genetic equilibrium to see how carrier individuals have context-specific benefits and consequences of carrying one mutant copy of the beta subunit. After reviewing the mechanics of CRISPR-Cas9, students examine the edits made to the blood stem cells that ultimately lead to a cure for sickle cell anemia and discuss ethical considerations. The case is ideally suited for an upper-level undergraduate course in genetics, but it could be easily adapted for a course focusing on ethical considerations of research into personalized medicine, gene editing, and the future of health sciences.