British scientists have received official permission to genetically modify human embryos.
The Francis Crick Institute in London could begin experiments within weeks after the Human Fertilisation and Embryology Authority (HFEA) approval yesterday.
The scientists want to deactivate genes in leftover embryos in IVF clinics to see if it hinders development.
It will be only the second time worldwide such a procedure has been undertaken and the first time it has been directly approved by a regulator. A Chinese team was widely criticised last year for similar experiments.
About 50 per cent of fertilised eggs do not develop properly and experts believe a faulty genetic code could be responsible.