Rhodesian Ridgeback - Ridge Genetics

Ridge Genetics

The genotype responsible for the ridge was recently found by a consortium of researchers at the Swedish University of Agricultural Sciences (Nicolette Salmon Hillbertz, Göran Andersson, et al.), Uppsala University (Leif Andersson, Mats Nilsson, et al.) and the Broad Institute (Kerstin Lindblad-Toh, et al.).

The only disqualification in the AKC standard for this breed is "ridgelessness". This term refers to the purebred offspring of heterozygous parental animals that do not inherit a copy of the ridge mutation from either parent and are, in effect, normal dogs without a ridged back. The most current research suggests that the ridge mutation is autosomal dominant with complete penetrance. However, while the few studies that have analyzed the issue do not agree on the incidence of ridgelessness within the breed, they all show a ridgeless rate significantly lower than 25%, which cannot be explained using the Punnett square model for single gene/two allele inheritance.

One possible reason for these studies to deviate from the expected 25% incidence of ridgelessness is inclusion of parents who were not heterozygous (possessing a copy of both the ridgeless and ridged allele) in the study. The inclusion of homozygotes (possessing two copies of the ridged alleles) would make the observed incidence be less than 25% when averaged across the population in the study. Since a molecular genetic test for the ridge gene does not exist, heterozygotes are detected by mating the animal in question to either known heterozygotes or known homozygous recessives (other methods exist such as mating to offspring, but result in inbred offspring) and a heterozygote is detected when a ridgeless pup is born. Note that 1) many matings are required to have a high probability of detecting a homozygous dominant (once a ridgeless pup is produced, the animal in question is assumed to be homozygous without question), and 2) more than one sire can produce the pups in one litter. The latter fact can cast doubt on the calling of male heterozygotes by this method and could possibly lead to the results shown in studies testing the mode of inheritance of ridgelessness.

Traditionally, many ridgeback puppies were culled at birth for numerous reasons, including ridgelessness. Contemporary breeders are increasingly opting for surgical sterilization of these offspring to ensure they will not be bred but can live into maturity as non-showing, non-breeding pets. Some breed parent clubs and canine registries in Europe have even made the culling of ridgeless whelps a requirement. It was pointed out on the BBC One investigative documentary Pedigree Dogs Exposed that The Rhodesian Ridgeback Club of Great Britain's "code of ethics", which is ratified annually by the Kennel Club states that "Ridgeless puppies shall be culled", and that "mismarked" puppies will only ever be sold on condition that they are never shown, and are neutered. The Ridgeback Club defended itself pointing to the statement that follows, "if a breeder finds this morally impossible the puppy shall be homed..." as indication that culling is not mandatory, but preferred. It was only after the publicity surrounding the promotion of culling that they reversed their code of ethics to say "no healthy puppy will be culled."