Over the summer, Sonja Prohaska decided to try an experiment. She would spend a day without ever saying the word “gene.” Dr. Prohaska is a bioinformatician at the University of Leipzig in Germany. In other words, she spends most of her time gathering, organizing and analyzing information about genes. “It was like having someone tie your hand behind your back,” she said. But Dr. Prohaska decided this awkward experiment was worth the trouble, because new large-scale studies of DNA are causing her and many of her colleagues to rethink the very nature of genes. They no longer conceive of a...