In a darkened lab in the north of England, a research associate is intensely focused on the microscope in front of her. She carefully maneuvers a long glass tube that she uses to manipulate early human embryos.
"It's like microsurgery," says Laura Irving of Newcastle University.
Irving is part of a team of scientists trying to replace defective DNA with healthy DNA. They hope this procedure could one day help women who are carrying genetic disorders have healthy children.