Most of you are undoubtedly aware that color and certain diseases such as progressive retinal atrophy (PRA) are inherited  that is, passed down from one or both the parents. However, you may wonder how a trait that does not appear in the dam's pedigree can suddenly turn up in a litter out of Ch. Jacob Hugelsberg. Is it inherited or just an accident? Surely, Jake has been used so often that someone would have noticed if the problem came from him.

Just how much of a role does genetics play in health, general conformation and temperament? Probably, you would like to know exactly what traits are inherited; but, once someone starts talking about "partial dominance" or "expressivity," you get glassy-eyed. The objective of this guide is to explain some of the basics of inheritance and how to use these concepts to breed healthier dogs — hopefully without losing you in complex technical jargon.

What Traits (or Characteristics) Are Inherited?

The answer is "almost all," from temperament to size and coloring, as well as genetic diseases like progressive retinal atrophy (PRA). Infectious diseases are not inherited, though the susceptibility to them may be, to a greater or lesser extent.

The occurrence of any particular characteristic depends on two factors: genetics and the environment. "Genetics" refers to the encoded information (instructions) controlling all biological processes that are carried within the cells of all living organisms. These encoded instructions are responsible not only for maintaining the continuity of a species (or breed), but also for many of the differences between individuals within a species or breed.

The environment also contributes to the differences between individuals. The relative contribution of genetics and environment is not the same for every trait. Some traits, such as color, are influenced very little by the environment. For others, such as temperament, the effect of the environment is much greater. Geneticists use the term heritability to indicate the proportion of the total possible variability in a trait that is genetic. However, when genetic differences are not the main source of variability, the heritability of a trait may be difficult to establish and may not be the same for different breeds. Therefore, I cannot tell you that the heritability of size, for example, is 70% (or whatever it may be).

Before moving on to a more detailed discussion of genetics, I would like to take a brief look at what is meant by "environment," in the present context. For a puppy, the first environment it encounters is that of the mother's womb. Is the mother well nourished, healthy, and free from stress? How old is she? Is this her first litter? How big is the litter? Once the puppy is born, it experiences a new environment, where it has to compete for food and attention. Litter size is still a factor. How much food does the puppy get? How much attention does it get from the mother, the breeder, and the eventual owner? Does it have a safe and healthy environment? Does it have other dogs to associate with? The answers to these questions define, in part, the puppy's environment.