Many domestic dog breeds have originated through fixation of discrete mutations 
by intense artificial selection. As a result of this process, markers in the 
proximity of genes influencing breed-defining traits will have reduced variation 
(a selective sweep) and will show divergence in allele frequency. Consequently, 
low-resolution genomic scans can potentially be used to identify regions 
containing genes that have a major influence on breed-defining traits. We model 
the process of breed formation and show that the probability of two or three 
adjacent marker loci showing a spurious signal of selection within at least one 
breed (i.e., Type I error or false-positive rate) is low if highly variable and 
moderately spaced markers are utilized. We also use simulations with selection 
to demonstrate that even a moderately spaced set of highly polymorphic markers 
(e.g., one every 0.8 cM) has high power to detect regions targeted by strong 
artificial selection in dogs. Further, we show that a gene responsible for black 
coat color in the Large Munsterlander has a 40-Mb region surrounding the gene 
that is very low in heterozygosity for microsatellite markers. Similarly, we 
survey 302 microsatellite markers in the Dachshund and find three linked 
monomorphic microsatellite markers all within a 10-Mb region on chromosome 3. 
This region contains the FGFR3 gene, which is responsible for achondroplasia in 
humans, but not in dogs. Consequently, our results suggest that the causative 
mutation is a gene or regulatory region closely linked to FGFR3.