The Rhodesian Ridgeback's distinguishing feature is the ridge of hair running along its back in the opposite direction from the rest of its coat. The ridge is caused by mutation (duplication of stretch of DNA sequence including several genes). The mutation is called simply a ridge gene and shows dominant inheritance. Rhodesian ridgeback may inherit two ridge genes (one from sire and one from dam), or only one ridge gene (from sire or dam), or no ridge gene from both of them.
Dominant inheritance means that if a puppy inherited ridge gene just from one parent, ridge is present on the puppy´s back. Dog with one ridge gene is called heterozygote (R/r). If a dog inherited ridge gene from both parents, then it is called dominant homozygote (R/R).
However, in the litter there may be ridgeless puppies. Ridgeless puppies are born to two heterozygotes (male and female dog with only one ridge gene). Statistically, in a litter of two heterozygotes there will be born 25% ridgeless puppies .
However, according to the test results in practice, it appears that the ridge genetics in Rhodesian ridgebacks is not so simple and is characterized by incomplete manifestation of ridge gene (more info here). This means that every dominant homozygote (R/R) has ridge. Also great majority (>95%) of heterozygotes (R/r) have ridge, but few (<5%) of heterozygotes are ridgeless. It might be biologically explained that ridge gene is suppressed (incomplete penetrance of ridge gene). and ridge is not formed on the back. All Ridgebacks who posses two ridge genes have ridge and those who lack ridge gene (r/r) are ridgeless.
Further, it was also observed the association between genetic disposition for the ridge and the occurrence of dermoid sinus. According to the research, dermoid sinus occurs approximately 5 times more often in dominant homozygotes. So, our test may reduce the incidence of dermoid sinus in Rhodesian Ridgebacks by a controlled selection of individuals for mating.
We have developed the genetic test, which distinguishes dominant homozygotes (R/R - two ridge genes) from heterozygotes (R/r - one ridge gene). Using our genetic test, a breeder may accuratelly predict birth of ridgeless puppies (see Table below).
If you are interested in our genetic test, you will find all the information in the section Order test. For further questions, please Contact us.