This is where you come in
There is a way that we can narrow down what genes we look at, but it involves lots of dogs and lots of genomes to analyze.
Looking at well-documented pedigrees allows us to more easily identify the mode of inheritance for a given genetic disease. For example, if a disease seems to be inherited from mother to son then that indicates the disease may be X-linked. This allows us to be better able to identify how breeding pairs can be created to minimize genetic disease.
Genome Wide Association Studies (GWAS)/ Linkage Studies
Comparing the entire genome across many dogs allows us to see what nucleotides are different and ideally, identify the genes that cause a genetic disease. If lots of dogs with a disease phenotype have one base at a certain location in the genome, while lots of healthy dogs have another, it would follow that that location in the genome should be studied further. However, in order to be sure that a location that seems significant is and not just a random point of natural variation, we need as many samples as possible.