Three-parent DNA treatment for rare defect raises debate

Three-parent DNA treatment for rare defect raises debate: When women have defective mitochondria, their children can inherit terrible, sometimes fatal problems. A new technology, pioneered in England, adds healthy cellular structure from a third person, meaning that children are born with DNA from three people. William Brangham learns more from Jeffrey Kahn of Johns Hopkins University and Marcy Darnovsky of the Center for Genetics and Society.