OK, for the breed right now that is a loaded question. According to the AKC standard and the new standard that goes into effect Oct. 1st of this year, yes, merle is an acceptable pattern in Chihuahuas. How did it come into the breed, no one knows. The one thing we do know is that merle is a dominant gene meaning you have it to produce it. It did not come into the breed as a spontaneous mutation, can't happen. Most ethical breeders/exhibitors do not mess with merle. There are a *handful* of breeders/exhibitors who are breeding it.