Consider the double helix: simple, elegant, efficient and damned curvaceous. The full map of humankind’s genes—3 billion steps on DNA’s spiral staircase—was completed in 2003. Next rung: pinpointing a specific gene that causes cancer, say,  and cracking its code. For a while, safety fears stymied experiments, but now the hunt is on. In May, Icelandic researchers found a gene that doubles heart-attack and stroke risk; a drug already exists to foil it. The helix shimmers with hope for HIVers, too: A study to fortify anti-HIV cells by inserting a gene is now recruiting ( And so we baby-step up the spiral, seeking and tweaking genes to make cleaner meds—and, someday, vanquish HIV.