Here is a little technical information about the piebald spotting gene (called MITF) located on chromosome 20. Evidently, both the piebald and the Irish spotting mutations are not directly inside the MITF gene, but are located next to the MITF gene, and affect its regulation and expression. Here are links to the articles for the scientifically inclined:
http://www.lsu.edu/deafness/Karlsson...%20piebald.pdf MITF and White Spotting in Dogs: A Population Study