Chinese scientists have produced healthy mice from two mothers, using stem cells and gene editing to create offspring without the involvement of male mice.
The mice created using this technique were even able to go on to have children of their own.
Publishing their results in the Cell Stem Cell journal, the researchers explained that they produced the mice by injecting stem cells from one mother into the eggs of the other.
They used a special kind of stem cell called a 'haploid' embryonic stem cell, which means that they contain 23 rather than the usual 46 DNA-carrying chromosomes (just like male sperm).
They also deleted a number of 'imprinted' genes from these cells, since such genes normally depend on being paired with a corresponding male gene to work properly.
And by combining these two processes together, they were able to produce healthy offspring from two females.
Just as impressively, the created mice were able to live to adulthood and have offspring of their own.
However, the Chinese scientists also produced mice from two male parents using a similar procedure, but all of these died within 48 hours of birth.
The researchers aren't entirely sure why this happened, although they are planning to develop their procedures and try again in the future.
Based at the Chinese Academy of Sciences, they wanted to understand why animals of the same sex can't have babies together.
Dr. Qi Zhou, a senior co-author of the research, explained, "We were interested in the question of why mammals can only undergo sexual reproduction.
"We have made several findings in the past by combining reproduction and regeneration, so we tried to find out whether more normal mice with two female parents, or even mice with two male parents, could be produced using haploid embryonic stem cells with gene deletion."
Other researchers agreed that the Chinese team's work will open doors in the science of reproduction and genetics.
"This study is shedding light on various aspects of mammalian reproduction and development and it is opening new avenues for future research," said Dr. Dusko Ilic, a researcher in stem cell science based at King's College London.
However, animal welfare groups spoke out about the study.
Speaking to The Sun, an RSPCA spokesperson said: "We are concerned about the significant impacts on the welfare of animals involved in this, and potentially numerous related studies in the future, even more so as experts in the field say there is no realistic likelihood of a direct medical benefit to humans."
And Dr. Julia Baines, Science Policy Advisor at PETA UK, said: "Whether genetic engineering is carried out on mice, sheep, dogs, or monkeys, it's a Frankenscience that serves only to increase animal suffering."
She told The Sun: "Animal mothers are subjected to surgical procedures in order to harvest their eggs and implant the engineered embryos, many pregnancies fail, and the animals who are born are commonly forced to live with unintended debilitating conditions, such as missing eyes or ears, skin ulcers, deformed body parts, deafness, seizures, and heart failure, to name just a few.
"Most people accept that genetically engineering humans is morally unconscionable, and doing the same thing to mice using stem-cell technology is just as reprehensible – it will not solve reproductive problems but will lead to misery for intelligent, sensitive beings."
But while the research will raise expectations that other animals could be produced from parents of the same sex, Dr. Ilic warns that it will be a long time before similar methods could be used to produce human babies from two mums or two dads.
He said, "To consider exploring similar technology for human application in the near future is implausible. The risks 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."
This story originally appeared in The Sun.