Britain has approved the use of a "gene editing" technique to modify human embryos for research purposes and allow scientists to understand the development of an embryo in its first seven days.
The government's Human Fertilisation and Embryology Authority gave the go-ahead for the technique to a team from the Francis Crick Institute in London, subject to approval by a research ethics committee.
"As with all embryos used in research, it is illegal to transfer them to a woman for treatment," the authority said.
The Francis Crick Institute said it wants to use the research, led by Dr Kathy Niakan, "to understand the genes human embryos need to develop successfully" and study the causes of miscarriages.
"Dr Niakan's proposed research is important for understanding how a healthy human embryo develops and will enhance our understanding of IVF success rates, by looking at the very earliest stage of human development - one to seven days," said Paul Nurse, the institute's director.
Discussing the institute's application earlier, Niakan said the technology "allows very specific alterations to be made to the genome."
"By applying more precise and efficient methods in our research we hope to require fewer embryos and be more successful than the other methods currently used," she said.
Embryos would be used solely for research purposes and would be "donated by informed consent and surplus to IVF treatment," Niakan said.
Chinese scientists made the world's first report of CRISPR/Cas9 gene-editing of embryos last year, saying they had attempted to alter a gene that causes a blood disorder.
Critics of the use of the technology have raised concerns that it could eventually be used to alter DNA to create "designer babies."