A gene called Tbx2 is required and adequate to make inner hair cells (IHCs) of the ear distinct from outer hair cells (OHC) and maintain the difference, a mouse study shows. The researchers show removing Tbx2 from embryonic IHCs results in their becoming mature OHCs instead of IHCs. Removing Tbx2 from IHCs after birth turns them into mature OHCs. The ability to specifically produce an IHC or OHC will require a gene cocktail, the researchers claim.