We’re a step closer to two men being able to have genetic children of their own after the creation of fertile mice by putting two sperm cells in an empty egg
By Michael Le Page
23 June 2025
Adult male mice that have two fathers and went on to have offspring of their own
Yanchang Wei
For the first time, mice with two fathers have gone on to have offspring of their own – marking a significant step towards enabling two men to have children to whom they are both genetically related. However, there is still a long way to go before this could be attempted in people.
Yanchang Wei at Shanghai Jiao Tong University in China achieved the feat by putting two sperm cells together in an egg whose nucleus had been removed. The team then used a method called epigenome editing to reprogram seven sites in the sperm DNA, which was needed to allow the embryo to develop.
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Of the 259 of these embryos that were transferred to female mice, just two offspring – both male – survived and grew to adulthood, making the success rate very low. Both then fathered offspring – which appeared normal in terms of size, weight and appearance – after mating with females.
Creating mice with two fathers has proved to be much harder than creating mice with two mothers. The birth of the first fertile mouse with two mothers, Kaguya, was reported in 2004.
Kaguya had to be genetically modified, but in 2022, Wei and his colleagues were able to create similarly fatherless mice using only epigenome editing, which doesn’t alter the DNA sequence. This same method was used to make the motherless mice.