The Canine Diversity Project
A. Pedigree Analysis PEDIGREE ANALYSIS TEST MATING DNA TESTSBefore any effective action can be taken to reduce or eliminate a genetic disease, its mode of inheritance must be determined (i.e. Is more than one gene involved? Is it dominant or recessive?). This is usually accomplished through the analysis of the pedigrees of affected dogs.
In Genetic Research Strategies: The Example of Canine Epilepsy, Dr. Barbara Licht and her colleagues discuss the role of breeders and owners in canine genetic research, and the importance of having data not only on affected dogs, but also on relatives and unrelated animals.
In an accompanying article, Pedigree Analysis: Bloat in the Standard Poodle, John Armstrong illustrates the difficulties that may be encountered in working with a partial data set.
B. Test mating PEDIGREE ANALYSIS TEST MATING DNA TESTSThough breeders would, understandably, prefer not to breed affected dogs, deliberate test matings are sometimes the only way to clarify ambiguous data.
Day Blindness in Alaskan Malamutes is an account written by Dr. Bourns for Dogs in Canada describing the discovery of the genetic disease and the test mating program.
The Bourns Test Litters for Dayblindness in Malamutes summarizes the actual data from their 1967 paper in the American Journal of Veterinary Research.
C. DNA tests PEDIGREE ANALYSIS TEST MATING DNA TESTS
DNA tests are available for a growing number of genetic diseases. There are two types:
- Direct tests that detect the actual mutated site. Dr. Mary Whiteley describes the basic principles of these tests in Genetic Testing: A Guide for Breeders.
- Linkage tests, which detect another genetic marker such as a repeated sequence (microsatellite) located close to the actual mutation. These may be used when the difference in the DNA sequence between normal and mutant is not known. (A longer description may be found at the OptiGen site).
Both types of test require only a small blood or tissue sample for analysis.
In cases where the mutant allele has reached high frequencies in the population, wholesale elimination of heterozygous carriers could have disastrous consequences for genetic diversity. For example, in the Doberman, the combined incidence of carriers and affected animals is about 80%. The article by Dr. George Brewer, DNA Studies in Doberman von Willebrand's Disease, should be read by all.Current tests are listed on the OFA (Orthopedic Foundation for Animals) site
and the AHT (Animal Health Trust) in the United Kingdom.