Though the 3 meters of DNA inside the nuclei of our cells looks like a jumbled pile of spaghetti, the genome is, in fact, pretty well organized. Now, scientists have discovered—using a modified version of the gene-editing tool CRISPR—that the location of DNA, not just the order of its base pairs, can make a critical difference in how certain parts of the genome work. The nucleus is dynamic, with everything—the chromosomes, the nucleolus, and so on—swirling around seemingly randomly. But in the past decade, researchers have realized that DNA on chromosomes inside can reposition itself in specific ways, ways that...