Who needs a Y chromosome? Scientists have found that "male" mice without the sex-defining chromosome can reproduce—as long as they've got two key genes from it. A team in Hawaii worked with mice lacking full Y chromosomes; instead, they had two genes, called Sry and Eif2s3y, inserted on other chromosomes. These mice were able to produce only immature sperm, NewScientist explains. They needed some help to reproduce: In an IVF procedure, researchers injected material from the immature sperm into eggs, the BBC reports.
That resulted in successful fertilization 9% of the time. The rate is far lower than the usual 26% for mice with the Y chromosome, but it still shows that mice without it can father healthy pups that can themselves reproduce. So does this mean men are barely necessary? Well, the rest of the Y chromosome is key to producing motile, mature sperm, researcher Monica Ward says. And a man-free planet would be "science fiction," she notes. But the findings could help some infertile men reproduce in the future. (Read more Y chromosomes stories.)