A genetic test for ridge disposition:


A genetic test for ridge disposition 


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. This feature is genetically determined and governed by simple inheritance which was discovered by Johann Gregor Mendel already in 1865. The presence of the ridge on the back is due to the fact that the ridgeback has a ridge gene in its genetic make-up unlike all other breeds. Every ridgeback dog ​​inherits two ridge genes from its parents (one from the mother and one from the father). The Ridgeback can therefore have either two, one or no copy of the ridge gene. In case that no ridge gene is present, the dog is ridgeless, thus without its typical hair running in the opposite direction on the back. Inheritance of the ridge gene is dominant, meaning that if a dog has inherited the ridge gene just from one parent, it will have a ridge on the back and in genetic terminology is called a heterozygote. If a dog has inherited two ridge genes from its parents, it is obvious that the ridge is present and such a dog is called a dominant homozygote.

     In litters there may appear ridgeless puppies which do not possess the ridge gene. These puppies can be born with a probability of 25% to two heterozygotes, therefore to a sire and dam that have only one gene for the ridge. For clarity, the individual crossing and combinations are listed in the table below. From the table, we can see, for example, that if a dominant homozygote (a dog with two ridge genes) is mated with any other ridgeback (even ridgeless!), the offspring will always have a ridge.

     Despite the numerous requests from ridgeback breeders, a genetic test capable of distinguishing between ridgebacks with one and two ridge genes was unavailable until recently. Of course, we could deduce that if a ridgeless puppy was born to two ridged parents, then both parents were heterozygotes (possess only one gene for the ridge). However, only a genetic test for the ridge gene can confirm that a dog has two ridge genes, and is therefore a dominant homozygote.

     This test is now available and was created at the Department of Genetics and Reproduction of the Veterinary Research Institute, Brno, Czech Republic. As the author of this test Dr. Miroslav Hornak notes: "It was not easy to develop the test and it was necessary to utilize a technique which can accurately detect the DNA sequence copy number of the ridge gene. This gene was discovered in 2008 by Nicolette H C Salmon Hillbertz from the Department of Animal Breeding and Genetics at the Swedish University of Agricultural Sciences, Uppsala, Sweden, but a genetic test that would be available to breeders was missing. Many thanks go to the Czech Rhodesian Ridgebacks Breeding Club (KCHRR) - www.kchrr.com and namely to Mrs. Stusakova who willingly cooperated and provided us with necessary genetic samples and also to
Dr. Vlasta Linkova for her optimistic approach and never ending enthusiasm".

    The genetic test can be performed on a blood sample (0.5-1ml collected into tubes with an EDTA anticoagulant), but is sufficiently sensitive when using a buccal swab sample.

    Determination of the copy number of ridge genes, and thus the genetic basis of the ridge, might be used by breeders for controlled selection of animals for mating and avoiding the birth of ridgeless puppies, which is probably of their primary concern. However, a genetic test can make a significant overlap to the prevention of health of Rhodesian ridgebacks. In this breed, a genetic defect known as Dermoid sinus occurs, which is a neurodermatological abnormality based on an incomplete division of the neural tube from the skin at a certain point, arising during embryonic development. Dermoid sinus poses an elevated risk of infection at the dermoid opening, leading to the formation of purulent abscesses, and due to a connection with the neural tube, can result in meningitis, paralysis and death of the dog.

     From the research it is known that there is a correlation between the copy number of the ridge gene and the incidence of Dermoid sinus. Unfortunately, we do not know the exact genetic cause of this abnormality, but it was found that the gene for the ridge is an unfavourable genetic factor for the occurrence of Dermoid sinus. This can be concluded from the fact that a dog possessing two copies of the ridge gene has an increased risk for Dermoid sinus.

    The genetic test for the ridge gene can primarily provide a very valuable correlation between the genetic basis of the ridge and the occurrence of Dermoid sinus. A project emerges in collaboration between the Veterinary Research Institute and the Czech Rhodesian Ridgebacks Breeding Club (KCHRR)
- www.kchrr.com, which would help to clarify the role of ridge genetics in the pathogenesis of Dermoids. Dr. Hornak said about the project: "Firstly, we will try to explain how the copy number of the ridge gene correlates with the incidence of Dermoids in a large sample of animals, which will tell us more about the genetic background of this anomaly. Furthermore, it will be necessary to identify genetic markers that are closely linked to Dermoid sinus occurrence since, according to all scientific data, the copy number of the ridge gene only increases the likelihood of Dermoid sinus development. If we succeed in shedding light on the genetics of Dermoid sinus and find the appropriate genetic markers, we can improve the gene pool and increase fitness of Rhodesian ridgebacks for breeding .

We are now introducing the genetic test to breeders and all information is accessible at the GenoCan project websites - www.genocan.cz

Mating combinations in Rhodesian ridgebacks

Parents

Puppies

Sire

Dam

ridged

ridgeless

RR

RR

 100%      (100% RR)

0% rr

RR

Rr

            100%      (50% RR, 50% Rr)

0% rr

RR

rr

100%      (100% Rr)

0% rr

Rr

RR

            100%      (50% RR, 50% Rr)

0% rr

Rr

Rr

              75%      (25% RR, 50% Rr)

25% rr

Rr

rr

50%      (50% Rr)

50% rr

rr

RR

100%      (100% Rr)

0% rr

rr

Rr

50%     (50% Rr)

50% rr

rr

rr

0%

100% rr

RR (ridge) - dominant homozygote (two ridge genes)

Rr (ridge) - heterozygote (one ridge gene)

rr (ridgeless) - recessive homozygote (no ridge gene)