Genome maps are essential for identifying disease genes. The current canine map is composed of several thousand markers, and as a result, has proven useful for localizing several disease genes. A much more highly refined map is necessary if we are to actually clone disease genes of interest (not just identify their location) and, subsequently, develop appropriate genetic tests. This proposal aims at developing the technology to do that, focusing on a test case on chromosome one, where two genes associated with hip dysplasia in the Portuguese Water Dog have been mapped. The goal is to determine the location and linear order of many hundred small variants called “”SNPs”” throughout chromosome one. The resulting SNP map can then be used 1) by ourselves to identify the culprit gene(s) in PWD and 2) by anyone studying hip dysplasia in any breed of dog to determine if the same chromosomal region that is mutated in the Portuguese Water Dog is similarly responsible for disease in other breeds.