Color Genetics 101

With every breeding, one plans to produce the best puppies.   To that end, in considering potential stud dogs the worst possible consequences of the breeding are weighed against the expected best and average.  With every breeding, the breeder learns more about their lines and sometimes unexpectedly finds genes that were unknown in the lines!  That is exactly what happened with our recent litters.
  In response to the questions I have received regarding the excess white and the piebald colorations that were produced in these litters, I hope the following will serve to explain how these colorations can occur "out of the blue".

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 Casey is a poster child for the excess white or "mismark".  In color genetics there is a gene responsible for the full white collar, chest and face blaze and white socks, called the Irish Spotting Gene.   Plus and minus modifier genes affect how much white the individual puppy will show.   Casey has inherited the Irish Spotting Pattern, and minus modifiers have allowed extensive expression of this gene as evidenced by her chest blaze and full white front legs and 1/2 white head.  Color genetic experts have suggested that the excessive white on the head may be another, heretofore undiscovered gene.

Casey is possibly also a "phantom merle" in that she has developed patchy color on her white ear and has what appears to be a merle spot on her colored ear. There is also the possibility that these are "ticking" which is a dominantly inherited gene that is not considered a color fault. 

Casey's extensive white is a disqualifying fault in the NAMASCUSA Breed Standard. This is because this form of white is due to a lack of pigmentation.  This lack of pigmentation can be responsible for hearing impairment and/or visual impairment if the lack of pigmentation extends to the inner eyes and ears.  Casey has been examined by an ACVO veterinary ophthalmologist and has no visual impairment. We initially planned to have her hearing BAER tested, but it is very obvious that she has full hearing.

Kola Bear (now Dakota) is a very good example of the piebald gene coming out, though neither Sumatra nor Bruce are piebald, and Bruce has not produced a piebald puppy before. Bruce however does have white stifles which may be indication of the piebald gene's presence.

The piebald gene causes  white body splashes  which is a disqualifying color fault in the NAMASCUSA Breed Standard.   Dakota is also an excess white as described above, and like Casey he passed his ACVO ophthalmologic eye exam and has full hearing.
The piebald gene alone is not known to be associated with any adverse health problems.

Cowboy has also inherited the piebald coloration, but does not have the excess white.  Although he also was examined by an ACVO ophthalmologist (all Firehouse puppies are), he was not at risk for hearing or visual impairment due to his coloring.

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These color patterns are not to be confused with the extensive white that can occur in a merle to merle breeding.  Homozygous merle puppies may be almost all white. The serious health problems that can occur in those puppies are a direct result of their carrying 2 copies of the merle gene.
Casey and Dakota are not homozygous merles. They are the product of merle to tri breedings.

 
 



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