UK scientists have been given the go-ahead by the fertility regulator to genetically modify human embryos. It is the first time a country has considered the DNA-altering technique in embryos and approved it. The research will take place at the Francis Crick Institute in London and aims to provide a deeper understanding of the earliest moments of human life. It will be illegal for the scientists to implant the modified embryos into a woman. But the field is attracting controversy over concerns it is opening the door to designer - or GM - babies.