In experiments designed to explore what makes it so difficult for some animals to reproduce with same-sex parents, the researchers said mice from two fathers were also born but survived for only a couple of days.

The results, published in the journal Cell Stem Cell, suggest some barriers to same-sex reproduction can be overcome with stem cells and targeted gene editing. But experts said there was no prospect of it being translated soon into humans for the creation of ‘gay’ or ‘lesbian’ babies.

“To consider exploring similar technology for human application in the near future is implausible,” said Dusko Ilic, a stem cell specialist at King’s College London who was asked to comment on the Chinese results.

“The risk of severe abnormalities is too high, and it would take years of research in various animal models to fully understand how this could be done safely.”

Some reptiles, amphibians, and fish can reproduce with one parent but it is challenging for mammals to do the same even with the help of fertilization technology.

The researchers, based at the Chinese Academy of Sciences, explained that in mammals because certain maternal or paternal genes are shut off during germline development by a mechanism called genomic imprinting, offspring that don’t get genetic material from both a mother and father might be developmentally abnormal or might not be viable.

To create their bi-maternal mice, a team of scientists led by Qi Zhou used cells known as haploid embryonic stem cells (ESCs), which contain half the normal number of chromosomes and DNA from only one parent.

Using gene editing techniques, the scientists deleted three imprinting regions of the genome from haploid ESCs containing a female parent’s DNA and injected them into eggs from another female mouse. This work produced 29 live mice from 210 embryos. The mice were normal, lived to adulthood, and went on to have babies of their own.

Making mice from two fathers was more complicated, the researchers said and involved modifying haploid ESCs containing only a male parent’s DNA to delete seven key imprinted regions.

The edited haploid ESCs were then injected — along with sperm from another male mouse — into an egg cell that had its nucleus, and therefore its female genetic material, removed. This created embryos containing only genomic DNA from the two males, and these embryos were then transferred to surrogate mothers. These pups survived for only 48 hours after birth.

“This research shows us what’s possible,” said Wei Li, who co-led the work.

The scientists said there are still obstacles to using such methods in other mammals, including identifying which imprinted genes need to be deleted. They said, however, that they hoped to explore the techniques in other research animals in the future.

Azim Surani, a germline and epigenomics specialist at Britain’s Cambridge University, said the work was impressive, but the “extensive genetic manipulation” involved meant it is not a plausible way to create human babies from same-sex parents.