Genetic interactions in the pigmentation pathway in dogs

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The focus of our research program is to understand the mutations involved in producing pigmentation patterns in dogs. This is an excellent teaching tool in genetics because the traits are visible and the dog is an animal that students easily relate to. Pigmentation is a complex trait that allows us to explore many principles of inheritance, well beyond classical Mendelian inheritance. We have studied several genes in the past few years and have now reached the stage where we can better tease apart gene interactions among these genes and try to determine how mutations can interact to produce new patterns that occur only if more than one gene has a mutation. A recent example of this is the pattern called grizzle in Salukis and domino in Afghan Hounds in which two genes must have a mutation, one in the promoter (ASIP) and one in the coding sequence (MC1R). We are also now able to better elucidate epistatic interactions involved in pigmentation. The concept of phenocopy has been discussed in classical literature but we have now discovered examples of how two distinct genetic mechanisms can lead to the same phenotype (i.e. a recessively inherited mutation in ASIP and a dominantly inherited mutation in DEFB103 can both produce black coat color). Our next objective is to study "modifier" genes. The classical literature in genetics has suggested that such genes will interact to produce subtle differences in phenotype.