Thanks to advances in gene editing and stem cells, scientists in China helped two male mice create offspring together, without any female DNA. The feat had already been accomplished with two female mice, but this latest advancement marks the first time two male mice have created offspring that were carried to full term.
This marks a major advancement, but it's not time to start lining up at your local fertility clinic just yet, guys: while the mice pups born from two females were healthy, and were even able to conceive their own offspring, those born to two male pups died shortly after their birth.
A recent article in National Geographic helps explain why the feat is more difficult with makes. One of the main barriers is due to a process called "imprinting," during the development of sperm and eggs, when "tags" attach to our chromosomes. In mammals, these tags vary by sex.
"For female mouse pairs, they had to delete three locations to get healthy young," according to the article. "For male mouse pairs, they had to snip seven regions."
For the female pups, snipping just these three regions allowed the pups to grow at a normal rate. Snipping the seven regions in males allows the babies to develop to full term, but it is not enough, yet, to allow the offspring to live much past birth.
An additional barrier: to make an individual, you have to have an egg. "Males don't have eggs," a developmental biologist helpfully points out in the piece.