Scientists in China have bred healthy mice from same-sex parents for the first time.
Researchers achieved the feat by altering stem cells from a female mouse and injecting them into the eggs of another female.
They also bred "somewhat unhealthy" offspring from two male mice, but the pups died shortly after birth.
The breakthrough marks the first time researchers have been able to overcome the barriers that prevent same-sex mammals from producing healthy babies.
Mice have reportedly been born from same-sex parents before but they had serious abnormalities.
The process used at the Chinese Academy of Sciences involved "substantial genetic modification" meaning it is "unlikely to be useful in humans for now".
The mice born from two mothers have now grown into adults and have had healthy offspring of their own via normal intercourse with a male.
Dr Tim Hore, senior anatomy lecturer at the University of Otago in New Zealand, said: "The researchers in this paper used genetic modification to alter the genes which are expressed in a parent-specific manner in mammals.
"In doing so they were able to artificially overcome some of the usual incompatibility between parents of the same sex, meaning they were able to create relatively healthy offspring with two mothers, and somewhat unhealthy offspring from two fathers that died shortly after birth."
Scientists have been trying to work out what it makes it so challenging for mammals of the same sex to reproduce.
Animals such as sharks, chickens and Komodo dragons can have children without a genetic contribution from a male.
The researchers in China have noted that there are still obstacles in achieving their feat with other mammals.
Dr Hore said: "The work does fall short of creating mammalian offspring from the same sex in the absence of substantial genetic modification, meaning it is unlikely to be useful in humans for now."
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He added: "In order for same-sex (human) parents to both have genetic contributions to their children in an assisted reproduction setting, it is likely another technological leap will be required.
"One possible approach is using 'epigenetic-editing' on haploid stem cells, essentially reprogramming the DNA of one parent so it looks like that of the opposite sex without altering any genetic sequence."
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