Dog Breeding Genetics – Maintaining Good GeneticsLast updated: August 5, 2022 by Marty Greer, Doctor of Veterinary Medicine
Genetics is the study of how traits are inherited. Genotype are the traits we can test DNA for, while the phenotype are the traits we see in the dog visually or with X-rays, eye exams, listening to the heart and so on. We manipulate these traits to get different dog breeds or colors. Genetics is also how we breed away from detrimental issues like hip, hernias and eyes. But how does this all work?
An example of Co-dominance or incomplete dominance is the merle gene in dogs. Heterozygous Mm desired merle color, while MM merle shows mostly white and often is blind, deaf or worse. The mm phenotype is normal color.
Dog Line Breeding Vs. Dog InbreedingCanine line breeding is the breeding of ancestors behind both parents. Dog line breeding concentrates the genes of specific common ancestors or sets traits such as color, coat or size. Dog inbreeding is the mating of close relatives such as parent x offspring, sister x brother. The public does not understand the importance of line breeding to strengthen specific traits and finds this unacceptable., However, without line breeding, we cannot improve the traits we find desirable. Line breeding and inbreeding increases homozygosis (aa or AA) in offspring.
Genetic disorders or traits can be caused by a single gene pair (monogenetic) or several pairs of genes (complex or polygenetic). We are most interested in polygenetic traits with variable expression. Hernias, hip issues and Progressive Retinal Atrophy (PRA) are examples of polygenetic inherited traits.
Polygenetic TraitsA number of liability genes must combine to cross a threshold and produce the affected individual. Both sire and dam carry a genetic load of liability genes. Polygenetic issues are difficult to select for or away from. A firm veterinary diagnosis must be established so we know what the issue is and that the diagnosis is accurate. Search widely in the pedigree to see if this condition exists with increased frequency in your line. Even if we do not know the inheritance, we can select away from the issue.
Rate Genetic and Congenital Disorders Based on SeverityOne way to manage a breeding program is to rate genetic and congenital disorders based on severity such on a scale of one through three. Level one is a minor disorder. These are conditions that are easy to live with or easy to correct such as umbilical hernias, distichia (extra eyelashes), entropion (rolled in eyelids), and retained testicle(s). AKC allows dogs to be shown in conformation who have had umbilical hernia corrective surgery done.
Level two are disorders requiring long-term management but that are not life-threatening or life-altering. This includes hypothyroidism, anxiety, and allergies. These require life-long medication and management but other than the associated costs, do not seriously impact the dog's quality or quantity of life.
Level three includes life-threatening, life-altering, or life-shortening disorders. This includes bad temperament, seizures, orthopedic disorders (hip dysplasia, elbow dysplasia, cruciate disease) and at some point cancers (when we can DNA test for these). These cancers will include lymphosarcoma, malignant histiocytosis, hemangiosarcoma, and osteosarcoma. Many people make excuses for bad temperament, but when a dog is a threat to humans, these dogs should never be in a breeding program.
The biggest problem with the level one disorders are that veterinarians and breeders can detect these at an early age. As a result, these pups are booted out of a breeding program before other disorders can be detected and eliminated. In many cases, by the time level two and three disorders are found in a dog or line of dogs, it is too late - they have already produced pups. In other words, the problem is that young dogs may be removed from a breeding program when they are diagnosed with a minor level one health problem, but they may never develop level two or three disorders and because of the minor problem they are thrown out of the gene pool. Then those that aren't diagnosed with level one, but have level two and three disorders that show up later in life are perpetuated. Once we have better DNA tests, we can do a better job of eliminating some of these disorders.
Each breed and breeder needs to establish what traits are triggers for them and what needs to be eliminated first. There is no perfect dog.
Maintain the Line and the Good GenesOur goal is always to maintain the line and produce fewer "bad genes" in each new generation than in the last. By selecting less affected offspring and replacing more affected parents, we remove or reduce the undesirable phenotype and genotype.
Maintaining your line is the goal, as well as eliminating phenotype issues. Your next sire family should have fewer liability genes than the average for your breed. With traits that are multi-gene inherited, finding a sire with no PRA or Hip Dysplasia genes for example is not possible. If you are seeing the trait, you have it in both the sire and dam and enough of these genes are coming together to cause the issue or phenotype in the puppy. The genes came from both sides and therefore a "common ancestor" concentrates the genes they contributed and likely the problem genes. Search the pedigree for a common ancestor that gave multiple genes to both sides of the pedigree, in order to avoid that line and guide you in your next sire selection.
In the past, we eliminated a line or tried not to breed the affected line but that was short-sighted as we eliminated good genes too. Maintaining genetic diversity of your population is essential for progress. If you just outbreed without working to eliminate the genotype, you will fail. You will deal with it again in future generations because what you did was just disseminate detrimental recessive genes through your line. The goal should be for each generation must have fewer liability genes than the last!
If You Cannot Select from a Defect-Free LitterBe sure you know the genetic defect and how to diagnose it if possible. Select a normal female who is free from phenotype (i.e. hernias or hips). Breed this female to a male who is from sibling-free breeding. Replace the higher risk female with quality, lower risk offspring and repeat the process. Each generation will have a lower frequency of liability genes yet maintain the desirable genetics of the line. You decrease the risk, and the phenotype will not show up in future generations.
Environment plays a role but defects will only show up if you have the genes for it. Poor nutrition can alter expression of musculoskeletal disorders such as hip and elbow dysplasia, osteochondritis dissecans (OCD), Hypertrophic Osteodystrophy (HOD), Legg Perthes and knee problems, especially in the growth phase. Environment can not cause issues if the puppy is not prone to the phenotype. It is so important to decrease the liability genes in your line!
Dog Genetics and Breeding Tips
- Welcome feedback from your clients on issues they are seeing.
- Request a veterinary letter so you know how they diagnosed the condition and that it is accurate.
- Get a game plan that includes dog genetic testing in breeding stock. Testing is once in a lifetime!
- Work with people in the breed that know the condition and eliminate it.
Genetics do not tell you what you will see. Genetics tell you what you might see. Improved genetics is not a sprint, it's a marathon. A consistent plan is always a winner!
If you have more questions on dog genetics and breeding, call us at 800.786.4751.
Donald Bramlage, Doctor of Veterinary Medicine, Former Director of Veterinary Services at Revival Animal Health
Donald Bramlage, Doctor of Veterinary Medicine, practiced veterinary medicine for 30+ years and is known for his work in managing parvovirus. He received his Doctor of Veterinary Medicine from Kansas State University in 1985. He served as Revival's Director of Veterinary Services from 2011 until his retirement in 2019.
The materials, information and answers provided through this website are not intended to replace the medical advice or services of your personal veterinarian or other pet health care professional. Consult your own veterinarian for answers to specific medical questions, including diagnosis, treatment, therapy or medical attention.