In 2013, scientists at MIT and at UC Berkeley optimized a way to use bacterial gene sequences to cut and change DNA at precise locations. The genome-editing system, called CRISPR, is cheaper and simpler than previous methods, and it has led to breakthroughs in diagnostics and the creation of more accurate disease models. And because it can permanently modify a living organism’s DNA, CRISPR technology may one day allow physicians to treat genetic diseases—anything from congenital deafness to...