(CNN) Researchers in China say they've bred healthy mice with two mothers using a new type of gene editing technology, a significant feat that may help researchers better understand mammalian reproduction but carries significant ethical and safety questions.

A total of 29 bimaternal mice were produced using 210 embryos in the study. They all were "normal, lived to adulthood, and had babies of their own," though they showed "some defective features," according to researchers at the Chinese Academy of Sciences.

This image shows a healthy adult bimaternal mouse who was born to two mothers with offspring of her own.

But not all the mice pups survived the experiment. Mice produced from two fathers only survived a couple of days after being born.

"This research shows us what's possible," Wei Li, one of the study's co-authors, said in a news release.

"We saw that the defects in bimaternal mice can be eliminated and that bipaternal reproduction barriers in mammals can also be crossed through imprinting modification," said Wei Li.

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