This exercise provides hands-on experience in visualizing and understanding the difficult concept of immunoglobulin gene rearrangment and isotype switching. Students loop, ligate (tape), and cut strips of paper DNA to simulate the looping and joining of heavy chain gene segments. Students begin with a strip of germ line DNA, rearrange the DNA, form a primary RNA transcript, process it into mRNA, translate a nascent polypeptide, and produce the final heavy chain. At the completion of this activity students will understand immunoglobulin gene rearrangements and isotype switching enough to start with nascent DNA and create any isotype of immunoglobulin.