Polygenetic is how many serious problems in dogs are characterized genetically. This means more than one gene is responsible for the condition's expression, and that means tracking the inheritance is more difficult and more frustrating than with simple dominants & simple recessives. Although it is certainly not precise, treating polygenetic situations as you would treat simple recessives is probably going to get you the best results as to controlling canine genetic disease, when your options for "proof" are limited. Certainly, both parents must be included as likely contributors to the disease. As a rule of thumb complex characteristics are polygenetic: hip conformation & CHD disease, head conformation and the resulting bite, construction of internal organs (that end in heart, kidney, etc. malformation or malfunction as well as normal function, of course). In some cases a single gene IS found to be the culprit, but in many cases inheritance is erratic and any particular form has not been documented, so these things get stuck into the "polygenetic" pile until they get sorted out. This does NOT mean they are "not genetic" because a certain proof of how they are inherited is lacking-that is more head in the sand tactics. If it occurs in a particular population (such as a certain breed or even bloodline) more often than in the general population, then, to be careful and conservative as a breeder, it must be treated with the caution of it being genetically inherited until proven otherwise. Anyone truly concerned with the breed is not going to dismiss the evidence it is LIKELY genetic to go on with a breeding program in denial they are carrying down certain undesirable (or even debilitating) traits.