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For the first time, mice are born to two male parents 

Tiffany Zhou | March 22, 2023
“Hopping Mice” by Stephen Michael Barnett is licensed under CC BY 2.0. To view a copy of this license, visit 

In early March, Katsuhiko Hayashi, a biologist at Kyushu University in Japan, presented his research on the successful birth of mice with two biologically male parents at the Third International Summit on Human Genome Editing at the Francis Crick Institute in London.

How was this novel feat accomplished?

Hayashi’s team of researchers took induced pluripotent stem cells from an adult male mouse, cultured them in petri dishes, and removed the Y chromosome. The cells were then chemically treated to duplicate the X chromosome and embedded into an artificial ovary to develop into egg cells. This particular process marked the first time chromosomes have been successfully manipulated to turn a male adult stem cell into an egg cell. Finally, the team fertilized the new egg cells with sperm from a male mouse, and implanted the embryo into a female surrogate mouse.

However, it’s important to note that only ~1% of the 630 total implanted embryos grew into healthy and fertile adult mice; this technique is still being improved in terms of both practicality and efficacy.

What is the future of this research?

Since this research is still in its preliminary stages, there is still a long way to go before the methods can be applied to generate human egg cells. Currently, a few challenges include improving the success rate of the gametogenesis process and successfully transferring the method to more complex species. For complex species such as humans, egg cells would need to be grown in the laboratory for a longer period of time, introducing a greater possibility of epigenetic errors and mutations.

Furthermore, the manipulation of human embryos involves multiple ethical and legal complications which would need to be addressed in tandem with the advancement of scientific research in the field. Despite these challenges, however, Hayashi and other researchers are optimistic about using this study’s methods to allow reproduction for people struggling with infertility, Turner syndrome, and LGBTQ+ couples.

Works Cited

Bartels, Meghan. “Mice with Two Fathers? Researchers Develop Egg Cells from Male Mice.” Scientific American, Scientific American, 15 Mar. 2023, 

Ledford, Heidi, and Max Kozlov. “The Mice with Two Dads: Scientists Create Eggs from Male Cells.” Nature News, Nature Publishing Group, 9 Mar. 2023,