Genetics

The defective puppy is not caused by one defective gene. It is the unfortunate side of our merle genes which produces the beautiful merle patterns. The defective puppy is the pure merle puppy, which averages one out of four in a merle to merle mating. Something we do not completely understand about the merling gene is how the gene breaks down the coloring in an otherwise solid dog, and also affects eye and ear development in the fetus. When the solid gene is present with the merling gene, the results are a sound merle dog. When the merle gene is joined with another merle gene (homozygous merle), a defective puppy is the result.

EXAMPLES:  M = Merle Gene, m = Solid Gene

Each sound merle dog carries Mm gene.

Each solid dog carries mm gene.

In an average litter of four puppies from a merle to merle breeding:

In an average litter of four puppies from a merle to solid breeding:

In litters from merle to merle matings, they will statistically average one defective, homozygous merle puppy out of four. This will vary from one to many defective puppies in a given litter. If you realize these puppies are going to be deaf or have eye defects, it is not too difficult to cull them at birth. This should be done as soon as possible after whelping since there is no reason to stress the bitch with nursing extra pups. If you cull all puppies with white off the blaze, collar, socks, white chest and belly patterns, there are no borderline pups. Defective, homozygous merle puppies are often primarily white with just patches of color, and nearly always have a lot of white on the head. Puppies with each eye surrounded with color, color over the ears, and no white on the body behind the shoulder should be sound. The patterns seem to be the key. Sometimes a puppy without very much white, but with mismarkings on the body, such as a stripe running up from the underside, will be defective.