Non Mendelian traits could be apportioned to the environmental effects. Whilst the female is pregnant, she could become ill. This illness would have an effect on the unborn pups. Similarly, incorrect feeding can have effect. Often white markings can appear when they shouldn't. These could be caused by the environment, not being caused by the genes would mean they are non Mendelian effects. Refer him to the Law of Filial Regression. Hope this helps him. I am not a geneticist, but I have studied it to a "lay" level prior to and whilst breeding and showing my dogs from 1976 through to the mid to late nineties.