Scientists have created what is believed to be the first genetically modified (GM) human embryo.
A team from Cornell University in New York produced the GM embryo to study how early cells and diseases develop. It was destroyed after five days.
The British regulator, the Human Fertilisation and Embryology Authority (HFEA), has warned that such controversial experiments cause “large ethical and public interest issues”.
News of the development comes days before MPs are to debate legislation that would allow scientists to use similar techniques in this country.
The effects of changing an embryo would be permanent. Genes added to embryos or reproductive cells, such as sperm, will affect all cells in the body and will be passed on to future generations.
The technology could potentially be used to correct genes which cause diseases such as cystic fibrosis, haemophilia and even cancer. In theory, any gene that has been identified could be added to embryos.
Ethicists warn that genetically modifying embryos could lead to the addition of genes for desirable traits such as height, intelligence and hair colour.
The Human Fertilisation and Embryology Bill, which will have its second reading this week, will make it legal to create GM embryos in Britain.