
Standards most often call for complete, normal dentition, but there are many exceptions, the abnormal almost always being recessive in nature. This is why you may occasionally find Shepherds with undershot mouths, but not Boxers with overshot or scissors bites. Indeed, Humphrey and Warner found full dentition to be dominant over missing teeth, and theorized the involvement of more than one gene. Yet the doubling up of recessives has produced many a German Shepherd Dog with missing teeth. That this is not a Mendelian trait is shown by the fact that if you breed a dog with one missing premolar to another with the same tooth missing, sooner or later that pair's progeny or line will have several missing teeth, not just that one. This is slightly similar (and perhaps the mechanism is, too) to the phenomenon of breeding slightly dysplastic or "fair-normal" dogs and coming up with more dysplasia and greater severity than in the parents, as well.