Embryo created using two women and one man

The researchers at Oregon Health & Sciences University said they are not using the embryos to produce children, and it is not clear when or even if the gene therapy technique will be put to use. Similar experiments in Britain, reported in 2008, led to headlines about the possibility someday of babies with three parents.

But scientists say the DNA from the second woman amounts to less than 1% of the embryo's genes.

The British government is asking for public comment on the technology before it decides whether to allow its use. One concern it cites is whether such DNA alteration could be an early step down a slippery slope toward ‘designer babies’.

Questions have also arisen about the safety of the technique.

An expert panel in Britain said in 2011 that there was no evidence the technology was unsafe but urged further study.

Laurie Zoloth, a bioethicist at Northwestern University in the