This article describes a 90-minute real-world lesson in which students use online bioinformatics tools to compare gene sequences between one wild-type and one type of eight hypothetical mutant Mycobacterium tuberculosis (Mtb) strains. Using bioinformatics online tools, students identify single-nucleotide polymorphisms (SNP)at http://www.genome.jp/tools/clustalw, translate each gene sequence to an amino acid sequence at http://exon.gatech.edu/genemarks.cgi, and determine if the SNP in the variant sequence will affect structure and function of the protein (antibiotic resistance or susceptibility). The activity ends with students writing a scientific explanation and providing evidence and reasoning to support their claim of antibiotic resistance or susceptibility. The article provides two appendixes: student learning objectives and student instruction and questions. A rubric for the assessment of student’s scientific explanation and an answer key for the eight strains are included. The article includes a link for downloading all background information, student direction, and DNA sequences for this lesson. http://www.stronglab.org/taylor. This activity was piloted in four traditional high school biology classes (9th and 10th grades) in an urban high school. Over seventy percent of participating students said that the lesson increased their understanding of the molecular consequences of mutations.