Black-and-Tan Rhodesian Ridgeback Genetics-Issues and Possible Solution
by William S. Rosenthal
Why should anybody care that there are black-and-tan Rhodesian Ridgebacks? The answer is complicated. The Rhodesian Ridgeback is a young breed, less than one hundred years old. It is a breed that was developed from numerous other breeds that were crossed with native African dogs. The breed’s origin is at best murky. When the breed standard was established in 1922, the acceptable colors included what we now call wheaten (in all of its varieties) as well as other colors that were later dropped. Black-and-tan, as far as we know, was never included in that standard. That is not to say that no black-and-tans existed then. That point, however, is still debated. Some breeders are willing to admit to litters that have occasionally thrown brindles and blues, but few will admit to black-and-tans. Perhaps that is due to the mistaken belief that to produce a black-and-tan, some RR bitch has been gotten to, “over the fence”, by a Doberman or a Rottweiler. The notion of polluting the breed in that way is anathema to Ridgeback fanciers. Therefore, the question of whether black-and-tans can be produced legitimately is vital.
There are also economic issues. Breeders who can claim a “purity” of line will be preferred by the purchasers of these dogs, as well as by those who wish to breed them. Consequently, only more successful and courageous breeders are likely to admit to having these odd colored dogs in their lines. There is a sociological aspect to this issue as well. The notion of purity of breed is a concept that some people hold to more than do others. The notion of what different breeds connote in society (not to mention varieties within a breed) is of some academic interest. An informative thesis about this is presented by Sandra Swart in a paper that is referenced at the end of this article (1). The breeds discussed include our wonderful Ridgebacks, as well as the Africanis and Boerboel. A careful reading of this thesis will make clear that we are dealing here with a sociological issue that goes well beyond the science of genetics.
There are aesthetic issues as well. The breed standard does not allow for black-and-tans, although that color is not a conformation disqualification, and black-and-tans can participate in agility, obedience, and coursing. One can assume, however, that members of the public that choose to own these dogs as well as those that breed them do so because they like the way they look. There is nothing wrong in preferring the standard wheaten varieties. It is a matter of preference and there is no arguing that point. There are, of course, people who have seen a black-and-tan, who think they are lovely and ask how they can get such a dog. I explain to them that it is just not likely. There are very few black-and-tan Ridgebacks produced. People interested in owning a Ridgeback are served best by seeking one of standard color.
A Little Genetics
What is a black-and-tan Rhodesian Ridgeback, and how did it get that way? (A question not unlike, “How did the leopard get its spots?”) To answer that question requires some information about genetics. However, fear not. I will not go over ground well documented by others who are more qualified. I will simply summarize and refer interested readers to the original sources. The answer, however, is relatively simple. Ridgebacks are colored by the Agouti series of alleles. Agouti mainly refers to the banded appearance of individual hairs. It is a trait that comes in many varieties. For Rhodesian Ridgebacks, those varieties range from a light wheaten color to a dark red wheaten color. The black-and-tan pattern, however, is part of the Agouti series. It is not unexpected, then, that this pattern occurs in Ridgebacks.
“The probable alleles at the Agouti locus, in order of decreasing dominance, are: Ay, aw, as, at and a. Therefore, at the top of the Agouti series then we have Ay, Sable - also known as 'dominant yellow' or 'golden sable' (or what we call wheaten). This results in an essentially phaeomelanic phenotype, but the hair tips are eumelanin (black). The extent of the eumelanin tip varies considerably from lighter sables (where just the ear tips are black) to darker sables - where much of the body is dark. Allele at, 'black+tan' is next. This is a primarily black dog but with tan (phaeomelanin) markings around the eyes, muzzle, chest, stomach and lower legs, commonly seen in hounds, Doberman's and Rottweilers”(1, 2). Note that at is recessive. That means that both parents must carry the trait in order for it to occur in their offspring. It also means that in its recessive form it cannot be seen. A dog carrying only one recessive at gene will appear as a standard colored Ridgeback, although there is some evidence that these dogs may appear darker, or have more dark hairs in their coat. “The Bernese Mountain Dog shows the effect of black-and-tan combined with white markings, often called tricolor” (4). Most black-and-tan Ridgebacks are actually tricolor.
There is some dispute about from where the tan point allele in the breed came. The historical record suggests that a number of different dog breeds were bred to the native African ridged dogs to produce the Rhodesian Ridgeback that we know today. Even near the years of breed standardization, owners were apparently still introducing other established breeds into the gene pool when they showed outstanding and desirable traits such as tracking, assertiveness, endurance, protection, etc. “According to Wellings, Cornelius Jr. stated, that the best dog his father ever had was out of a Collie bitch. As Halmi put it, the Collie crosses ‘could cold track... run like the wind, and to their ancestors´intelligence had been added a subtle new cunning at rounding up grazing animals. They retained the Hottentot (Khoikhoi dogs´) instinct for hunting together in a silent pack.’ It seems that the principal crosses used with the Khoikhoi dogs were Greyhound, Bulldog and Pointer. But it´s known from Selous that in 1885 Nellis had a deerhound-like dog, - in other words a large, rough-coated Greyhound. The data also supports statements, that Nellis used Airedale and Irish Terriers and Collies. He also used the terriers and bulldogs-breeds which we know are certainly part of the Ridgeback gene pool” (5). Others have suggested that Bloodhounds were included in the mix, which along with Collies, some terriers, and some greyhounds could account for the black-and-tan at alleles in the gene pool.
Elsewhere, Helgesen includes an account of Trooper Mocke's report of his sojourn with VanRooyen (p.73). "....Cornelius VanRooyen (had) informed me that the establishment of this breed is strictly due to the importation of two grey-black bitches by Fredrick Selous!" (he meant Helm, Ed.) "These bitches were crossed with his ordinary ‘Boer hound’ hunting dogs, the result of which was eventually the ‘Ridge-Backed’ lion dog as we know it today….He described the two ‘grey-black bitches’ with curly hair over the body and yellowish buff legs and points"(5). This pattern is likely the black-and-tan of the Agouti series that was diluted, as in some Doberman dogs.
Solutions-Or, When is a Problem Not a Problem?
In some quarters of the Ridgeback community there seems to be an irrational belief that black-and-tans are a scourge only recently visited upon the breed. Both the history of the breed and the genetics of dog color argue against that view. Writers about the breed discuss the occurrence of black-and-tans, and other colors, going back at least thirty years. As to whether it is a problem or not, Willis (in Nicholson and Parker) states, “Essentially, as a mainly one-colour breed, colour inheritance is not complex in this breed and the exceptions (livers, Grey Ghosts, brindles and black-and-tans) will be relatively rare” (3). Just how rare it is difficult to say since breeding practices influence the incidence of black-and-tans. We do not know the incidence of black-and-tans because they are not usually registered and are often culled. In fact, at least one European Ridgeback organization requires culling in its code of ethics, “Pups with dermoid-sinus, absent or multiple crowns, colour not of standard or ridgeless should be culled at birth.”[Italics mine] In the United States, many breeders frown upon culling for conformation. It is, in fact, an unnecessary solution to removing a dog from the breeding population when low cost spaying and neutering is readily available. Not to mention the fact that breeders can increase income by putting these dogs out as pets with spay and/or neuter contracts.
The remaining question, particularly of interest to breeders, is how can the occurrence of black-and-tans be reduced or eliminated? First, the extent of the problem must be estimated since it cannot be determined exactly. If black-and-tans were permitted to breed randomly with other Ridgebacks, eventually a stable and predictable rate of occurrence would emerge. Since random breeding is not a factor, we need to ask what will be the incidence if all black-and-tans are removed from the breeding gene pool, either by culling or spay/neutering. The answer is that the rate would diminish dramatically, but never reach zero. The stable rate would reach about .25% (one quarter of one percent) (4). To put that in perspective I have relied on some statistics compiled by Clayton Heathcock (6) from AKC breed books and registrations. There appear to be sufficient Rhodesian Ridgeback litters registered each year in the United States to account for about 4000 dogs whelped yearly. That includes only registered breeders. Over ten years that would produce about 40,000 animals. At a rate of .25%, we would expect to see about 100 black-and-tan Ridgebacks over ten years, or about ten per year. I, personally, know of only a dozen or so over the past ten years. At any rate, I see no evidence of an “explosion” of black-and-tans.
Could the rate be further reduced, or even eliminated in a particular line? Probably, but in the absence of a reliable DNA marker for black-and-tan, Draconian measures are required. One would have to remove not only black-and-tans from the breeding pool, but all of their siblings and parents. Close inbreeding could mostly likely avoid the occurrence of black-and-tans, but at what cost? Further restricting the gene pool of an already highly inbred breed is likely to result in unintended consequences, such as increased health problems. For the overall health of the breed, I would argue that breeders should welcome the occasional occurrence of non-standard colors as evidence that the gene pool still bears some connection to the original lines that founded the breed in southern Africa.