At top and bottom left are two mice that have disabled copies of Hoxb1, a gene that controls the nerves needed for facial expressions. When a puff of air was blown into the face of the first mouse (top right), it couldn't blinked, wiggled its ears or pulled back its ears. The mouse that had a piece of Hoxb1 combined with Hoxa1, however, could react, thanks to the reconstructed gene. Credit: Petr Tvrdik/University of Utah