When potential owners come to me for a puppy, one of the main requests is they want to guarantee they get a healthy dog. Unfortunately no breeder, reputable or not, can guarantee this, due to the mode of inheritance. All we can do is our best and breed from healthy dogs. Having a healthy dog is also very much about how they are raised and cared for once they leave alongside genetics and bad luck. What is hidden in their genes, is another matter.
An interesting article below.
Written by Dr Malcolm B Willis
A little more on Polygenic traits:
There are some simple inherited traits in dogs, e.g. coat colour, coat length, ear carriage, presence or absence of hind dew claws, eye colour, some diseases and the like. When dealing with simple traits then you can make reasonably accurate predictions as to what will happen when breeding. However, many of the most important traits are not inherited in this simple fashion. Traits like fertility, temperament, breed type, height, weight, shoulder angle and several defects and diseases are complex in their mode of inheritance and are frequently affected by the type of environment in which we rear the dog. If, for example an Irish Setter is genetically red, then he will be red in coat colour regardless how well or how badly we feed him. But the kind of temperament he inherits may be modified by the way we socialise and rear him - such that he could finally exhibit a character very different from that which might have been expected. The same is true of his height and weight, badly reared he could be so drastically altered in conformation as to appear quite different from what he was bred for. Such characters are know as "polygenic traits" They are essentially produced by a series of genes which individually have a very slight effect, but which together make for very large differences. Not all polygenic traits are equally controlled by genetics. Some are more a question of environment, others more a question of genes and others fall between the two. Reproductive traits like litter size are basically genetic, but have a very high environmental component such as the size and the age of the dam, the type of nutrition, the stage of mating and a host of other things will all influence the eventual litter size. The extent to which a character is under genetic control is called heritability. Unfortunately, very few canine traits have had their heritabilities assessed for them, therefore we must make some educated guesses for them based upon our knowledge from other species. Genetically traits litter size, puppy viability, for fertility itself are likely to be low in heritability - less than 25 % and probably more like 10%. Things like Hip Dysplasia are 25% - 40 % under genetic control.
(Excerpt - written in 1977 by Dr M B Willis)
