Russia is an example of a hidden merle. She was born with very faint merle markings and they faded as she aged. She has a very slight blue left eye and her sire is a merle brindle who is not from a merle to brindle breeding. In other words. Both merle and brindle can pop up on a dog even with neither of the parent being an actual brindle.

A merle chihuahua should not be bred to another merle chihuahua ever! The gene that causes merle also causes blindness and deafness in dogs. It is usually when the white hits the eye or ear areas of the dog that make it blind or deaf. Breeding merle chihuahuas can be one of the most exciting patterns to breed but should also be taken very seriously. All cream or fawn dogs from merle breedings should be bred to non-merle dogs to see if they have the pattern. Seeing as how Gen-Mark testing closed its lab I don't know if there are any other tests that specifically test for the merle gene in dogs. Beware of any one who says the merle gene is carried! It is not carried and the dog has to be a merle to pass merle. Non merle dogs from merle lines do NOT carry the gene and are not able to pass it on unless they are bred to merles. Non-merles of merle breedings can safely be bred to merles once it is proven that they are not merles.

Eye color:

Just because a dog has a blue or other lightly colored eye does not mean it is a merle. While is most cases it is a merle, there are some cases in which it is not. Chocolates and blues are known for having lighter colored eyes. Don't let any one fool you into thinking that because a certain dog has blue or green eyes or one of each that it is a merle dog.

Merle to Brindle breedings:

There is no genetic reason why a merle dog should not or can not breed to a brindle dog. Most breeders strictly rule against it because brindling hides merling and in a litter where one gets brindles some are not really sure if they carry the merle gene being that they are merle but the brindling is hiding it. Merle to Brindle breeding is also known to cause "mud" meaning that the brindling and merling on a dog make it look not as flashy as a definite merle or definite brindle. I have yet to see an ugly merle/brindle dog and find them quite beautiful actually.

Marking Merle On AKC Paper work:

Any dog of merle breeding thought to be a merle should automatically be marked as "Merle Markings" when registering it. For example a chocolate and tan with merle markings should be marked "072" Chocolate & Tan and "035" Merle Markings. Doing this can help insure that merles are clearly noted in pedigrees and possibly prevent accidental merle to merle breedings from occuring.