If two merle dogs are bred, puppies can possibly inherit a merle gene from each parent creating a puppy with two merle genes. Names for this genetic combination are: lethal white, double dilute, or double merle.
The coat appears primarily white with small amounts of very faint grays or silvers since there are now two merle genes to wash out the color
While it can be quite beautiful to see, the lack of pigment in a double merle indicates there is no melanin wherever the areas with white coat occur on the body.
It is this melanin which allows the eyes and ears to develop normally while the puppy is a fetus.
the melanin, the eyes may develop very small, nonfunctional or even non-existent.
The puppy may be born blind even if the eyes are a normal size. Without the
melanin in the inner ears, there is also the possibility of deafness.
It is fascinating to me to see the link between two such traits of melanin and nerve development that I would intuitively think were unrelated.
it’s an accidently breeding as when a merle dog is bred to a cryptic merle. A
cryptic merle is a dog that carries the gene but expresses the merling so
insignificantly as to go unnoticed by the owner / breeder until pups are
whelped and there’s a white puppy in the midst of normal colored dogs.
Some show breeders will deliberately do this type of breeding in order to produce the double merle. Then, with the double merle bred to a tri or bi-black, they are
And while I’m all for a beautiful coat color, it isn’t something that I value so much as to take the chance of producing a deaf, blind dog. Quite honestly, coat color is pretty darn low on my priority list of traits I’m breeding for. But I make no judgments about other breeders programs.
is not to undervalue the spirit and the personality of any Sheltie, double
merle or not. A blind, deaf dog exhibits an immense amount of courage and grace
living in such a limited world.
There is a modifier of the merle gene which is the harlequin gene. This gene will turn the areas that are merle (dilute grays or silvers) into pure white.
Unlike the double merle sheltie, this genetic combination doesn’t affect the function of eyes or ears in spite of all the white.
is a dominant gene but is extremely rare in Shelties and may be non-existent at
this point in time.