In order to make the mice daughterless, Threadgill’s team introduced an additional modification. They attached to the t-complex an extra copy of Sry, a gene that is normally found on the Y chromosome and which determines whether a mammal turns out to be male. If the drive operates as intended—something that should be clear inside of a few weeks—more than nine in 10 mouse pups could inherit Sry and have male sex organs. Released in large enough numbers on an island, the daughterless rodents could, over the course of several months to a few years, result in a mouse population that is, so to speak, all Mickey and no Minnie. Then the mice would die out.