Pedigree Analysis
Before 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.
Test mating
Though breeders would, understandably, prefer not to breed affected dogs, deliberate test matings are sometimes the only way to clarify ambiguous data. One of the most thorough series of test matings done for such a purpose was that of
Rubin, Bourns and Lord for dayblindness in the Alaskan Malamute.
Because of the time and expense, test matings have not generally been used for routine testing.
Nevertheless, for a time, the English Kennel Club adopted a policy that allowed registration of
Irish Setters only if they had produced at least six normal and no affected pups in a mating with
a known PRA-affected animal (Willis, "Genetics of the Dog", p.223). This should have detected
98-99% of the carriers (Willis, p. 356) and was effective in reducing the incidence of PRA.
Direct tests
Now, a direct DNA test is available for PRA in Irish Setters and for a few other genetic
diseases. In "Genetic Testing: A Guide for Breeders", Dr. Mary Whiteley
describes the basic principles of these tests.
Though only a few such tests have been developed, research is progressing on many more. 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.
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e-mail: jbarm@uottawa.ca
