The trillions of cells in the human body can be categorized into hundreds of specialized cell types. All of these cells arise from the original fertilized egg and contain the same DNA. Differences among the cell types arise because cells selectively express some genes but not others. In this activity, students will explore how cells utilize transcription factors and enhancer regions to express different genes. Students who complete the activity will be able to: (1) explain and illustrate how cells that contain the same DNA can produce different proteins; (2) predict the activity of genes based on the presence of relevant transcription factors and enhancer regions; (3) Form an argument and reach a conclusion supported with evidence from the Models and from knowledge of molecular biology. [Process goal: critical thinking]. Level: Undergraduate Setting: Classroom Activity Type: Learning Cycle Discipline: Biology Course: Upper-level Course in Biology Keywords: gene, promoter, enhancer, transcription factor, coding region, DNA, messenger RNA, protein, RNA polymerase-II, genome equivalence, differential gene expression