There is a distinct genetic advantage of crossbreeding purebred dogs. Combining two breeds from unrelated gene pools results in what breeders refer to as “hybrid vigor” and geneticists call “heterosis”. “Not only is heterosis related to a decrease in the incidence of genetic defects, but also to an increase in traits like fertility, survival, and growth rate,” says Denny Crews, Jr., Ph.D., genetic research scientist. Purebreds that have been subject to generations of inbreeding are susceptible to genetic flaws such as hip displasia, thyroid conditions, eye problems, deafness and high-strung or aggressive temperaments, among many others. “After several generations of inbreeding, recessive genes which normally occur at very low frequency begin to accumulate within a breed and the likelihood that a puppy (will receive a copy of the defect gene from both parents) increases and the genetic defect expresses itself in the puppy,” “Out breeding (mating within the same breed to unrelated lines) or crossbreeding will reduce the incidence of genetic defects…”