Using a mash-up of stem cells and cloning technology, a team in Beijing claims to have generated mice with same-sex parents.

What they did: Sexual reproduction usually involves a sperm and an egg. Each brings 23 chromosomes to the party. The baby’s cells then have 46.

To make two-mother mice, the team first generated stem cells from a female mouse with half the usual number of chromosomes (23 instead of 46). Then they injected such a cell into an egg. It played the role of sperm, and some healthy pups were born.  

The team from the Chinese Academy of Science, which describes their work in the journal Cell Stem Cell, also managed to make mice with two fathers, but that took additional steps, and the offspring were none too healthy. Those pups were swollen, had unusually large tongues, and died young.

Why they did it: The exercise is mostly scientific so far, and there’s no intention of using this technology in humans. 

Right now, it’s far too complicated, and not all of the offspring survived. Instead, scientists say they did the work to understand more about reproduction itself. This kind of asexual reproduction happens in some corners of the animal world, but not among mammals. To make it work, the team found they had to delete several chunks of the animals’ genomes—including genes that would normally stop same-sex reproduction from occurring. 

The future: One day—if this technology matures—it might be that possible for two men, or two women, to reproduce together. But it will take a lot more work.