This happened in Germany in the late 1800's, when a handful of dogs descended from a Boxer and a mixed breed dog that was a cross between a Bulldog and a Schnauzer. Since another breed was introduced into the bloodline, they were not purebred.
Sometimes, breeders who claim to be breeding solid blacks often use the above incident as "proof" that there is such a thing. However, it quite clear that the dogs were not
purebreds and that the coloring came from another breed…They were quickly eliminated from the Boxer gene pool and the issue was settled.
At that time in Germany, the Munich Boxer Club strictly controlled the breeding of Boxers. A dog had to meet conformation and working standards before it could be bred. In 1925, the standard was changed so that a black coat was not an accepted color.
The Munich Boxer Club did not want black Boxers, so they did not allow them to be bred. It's possible that some "unapproved" breeding went on - but these dogs would NOT have been registered with the Club, so would not have been part of the gene pool that has come down to us today.
The question, then, is this: If the original black coloring came from a Schnauzer, and black Boxers (not purebred) from this cross became extinct in the early 1900s, why do some people insist that this coloring
still can appear?
There are several elements that prove that the black gene that was created in that crossing in the late 1800’s does not exist anymore:
- The trait has not been passed down – The proof of this is that the color black in Schnauzers is a dominant trait - a dog that has even one copy of the gene will be black, so a non-black dog could not be carrying or have the hidden the gene.
- While mutation is a possibility, the odds of it are enormously high - and the odds of it happening in several separate breeding populations are astronomical - enough so that we can safely rule out mutation for the majority of black Boxers out there.
The only viable option, then, is the genetic influence of another breed. In other words, any solid black dogs are not purebred.
There have been claims of a recessive black coat color gene in Boxers, but those making the claim also state that recessive black is fatal in those dogs.
This means that a puppy with two copies of the recessive gene for black coat color would not survive. However, there is no documentation to support this theory, and it has been discounted by breeder-geneticists.