Advantages of Mixed-Breed Dogs
Conceptually, puppies inherit two genes for every characteristic; one gene from its mother, and one gene from its father. If a puppy receives a defective gene from one parent and a normal gene from the other parent, the normal gene usually governs the characteristic and prevents the health problems associated with two defective genes. This concept of one gene exerting influence over another is called dominance. Although there are exceptions, normally a healthy gene will exert dominance over a defective gene (called the recessive gene) and the dog will not have the disease associated with the defective gene.
But if a dog has one defective gene and one healthy gene this dog is said to be a carrier of the disease. This is because although this dog will probably not inherit the problems associated with the disease, it can pass on the defective gene to its offspring. If the other parent also has one defective gene (it is also
But purebred dogs have a smaller assortment of 'normal' genes to 'match up' with and express dominance over defective genes. Many purebred dogs share the same defective recessive genes. Here is why this is important. Consider this example, in a dog breed that suffers an eye disease, many of the dogs in that breed share the same defective recessive gene that causes the eye disease. When two purebred dogs each contribute the same defective gene to their puppies, those puppies then have two defective genes responsible for the eye disease which results in the puppy inheriting the eye disease. This eye disease could then lead to the puppy going blind as an adult.
All dogs have defective genes. However, when mixed breed dogs mate, or dogs of different breeds mate, they normally have many more normal genes between them than defective genes. Therefore, when the offspring inherits one defective gene from one parent it is much more likely to inherit a second normal gene from the other parent. Because the defective genes don't match, the dog usually doesn't experience the related health problem. In most breeds of purebred dogs, the same defective genes are far more common and, as a result, more likely to match. This explains why mixed breed dogs are healthier than purebred dogs.