Just a bit of idle mutilation by scientists who were once little boys pulling wings off butterflies. This creepy step is not coming anytime soon (or distant) to a gay couple near you, for the same pesky reasons of human complexity that have foiled the cloners of men rather than mice.
Try the Wall St Journal for an outline of this "weird" experiment (to use the word of the principal mutilator); or get as much explanation as you would ever need from Dr David Prentice at his FRC blog.