The ridge of hair along the spine which characterizes the Rhodesian ridgeback breed is caused by a dominantly inherited mutation which also predisposes the dogs to a congenital disease called dermoid sinus. The scientists discovered that both the ridge and the dermoid sinus disease are caused by a mutation which contains extra copies of four genes. This mutation explains why the hair on the coat at the ridge grows in the opposite orientation compared to the rest of the coat.
– If the mutation is inherited from both parents, the risk is increased that the puppies develop the congenital disease dermoid sinus, says Nicolette Salmon Hillbertz, PhD student at Department of Animal Breeding and Genetics, Swedish University of Agricultural Sciences (SLU), who has been responsible for the ridge studies. Dermoid sinus is a major problem in the Rhodesian ridgeback breed and if ridgeless dogs are used as breeding dogs in the future, the problem with dermoid sinus will be largely eliminated, says Göran Andersson, who together with Åke Hedhammar, SLU and Leif Andersson and Kerstin Lindblad-Toh, Uppsala University, are leading a research group focusing on dog genetics in Uppsala.
Different types of white markings are common among several different dog breeds (see Figure 1 and Box 1). It is very likely that humans actively have selected for the presence of the white markings for several thousand years. By the Middle Ages, different patterns of white spotting were already common. Hunters might have bred dogs with white colour because they were easier to see, or maybe people preferred the white spotted dogs for purely aesthetic reasons. ”It is particularly exiting that with the results we are now reporting we can start to reconstruct the evolutionary history of this trait in dogs” says Leif Andersson, who works both at Uppsala University and SLU. ”We can show that different types of white markings are due to different combinations of several mutations in the same gene (MITF). This suggests a very strong selective pressure acting on this trait.”
– There are more than 350 known genetic diseases in the different dog breeds. In a particular breed like e.g. Rhodesian ridgeback, between 8 to10% of the dogs are affected by the disease dermoid sinus. We reported this already in an earlier study, says Göran Andersson. The excitement with the new results is that we now know exactly the nature of the mutation that causes the ridge and we can use this knowledge to breed healthier dogs. By utilizing the knowledge about the dog genome sequence we have the tools needed to find the disease-causing mutations for many different genetic disorders. The new knowledge can be applied in practical breeding of dogs to eliminate disease genes for many diseases. Therefore, the geneticist is the dog’s best friend, says Göran Andersson.
– The findings we are reporting is the result of an intra-disciplinary collaboration between Swedish and US scientists, says Göran Andersson. The knowledge about the dog genome and the array of genetic markers that has allowed these studies were developed at the Broad Institute at MIT and Harvard University, Cambridge, Massachusetts, by research directed by Kerstin Lindblad-Toh.
The geneticist is together with the veterinarian the dog’s best friend and the new methodologies will have major impact in dog breeding to decrease the incidence of inherited diseases, says Åke Hedhammar whom together with Henrik von Euler are responsible for the veterinary medical aspect.
– We are now using these methods to search for genes underlying both cancer and immunological diseases, says Kerstin Lindblad-Toh. I believe that the strong collaboration between the groups at SLU and Uppsala University can in the long term lead to new discoveries that will improve the health in both dog and man.