The Big Genetics Experiment by Ann Chamberlain

I first met Rhodesian Ridgebacks in 1965 while living in Rhodesia.  I honestly cannot remember seeing more than one litter with ridgeless in the four and a half years I was there.
 
When I came back to the US in 1969, I met several of the original breeders in the US and many stories were shared around.  One was that a ridgeless pair had been bred (whether by accident or on purpose was never mentioned).  Since we normally put the ridgeless pups down then, it would seem if the story were true that it had to be intentional, if it ever happened at all.  The story was there was a least one ridged dog in the litter.  That has stuck in the back of my mind ever since.
 
Later I met another breeder who said she was tired of throwing out the best dog in her litter because it was ridgeless.  She intentionally bred one ridgeless bitch because, in terms of conformation, she was by far the most correct dog in the litter.  One of the resulting pups went on to become a big show ring winner and I think others also earned their championships.
 
During my years of breeding, I never had a ridgeless pup (nor a dermoid), until I bred outside my line.  That female had 12 pups, of whom 6 were ridgeless.  I was shocked.  I began to think about the stories I had heard lo those many years ago about the ridgeless dogs being bred.  Then came the great announcement at the World Congress that “the gene” for the ridge had been discovered.
 
When I read the paper Nikki Salmon-Hilbertz had published in Sweden, I was fascinated.  I bred both my older girls to males that were not closely related by any stretch of the imagination and lo and behold, each of them had half ridgeless dogs in their litters.
 
Of course, in both cases, the nicest female in the litter in terms of conformation was the ridgeless one.  At that point, I decided to breed both of them, pending health checks of course.  I searched for male that had not sired ridgeless, despite being bred to several different lines.  Several well-respected breeders stepped up, volunteering their dog.  I also pleaded with a couple of breeders to keep a ridgeless male intact so we could breed ridgeless to ridgeless.  I was successful on both counts and greatly appreciate these breeders who understand what I am trying to do and why.
 
I then contacted Dr. Hilbertz to ask if she would be interested in the DNA from any pups from these breedings, to which she responded with an enthusiastic yes.  So here we are.  The girls are now old enough to be bred and we are proceeding with our experiment.  One ridgeless girl has been bred to a dog that has not sired ridgeless and the other will be bred to a ridgeless male.
 
As a scientist, I do not think the ridge genetics are simple Mendelian genetics, which is the way “the ridge gene” has been understood by most people.   Saying the dog is RR, Rr, or rr does not explain short ridges, comma ridges, or multi-crowned ridges.  Therefore, the great genetics experiment has begun.
 
In a paper published by Clayton Heathcock, he too has raised the question of how simple is this?
 
“The ridge in both Rhodesian Ridgebacks and Thai Ridgebacks is caused by a
mutation on chromosome 18 in which a stretch of the DNA that is 133,400 nucleotides
long has become duplicated. This duplicated segment of chromosome 18 has been called the “ridge gene”, but the duplicated segment includes four known genes and part of a fifth. It is presumably the presence of multiple copies of one or more of these genes that is responsible for formation of the ridge during embryonic development, by a mechanism so far not known.”
 
When you have multiple loci involved in the phenotypic expression of the ridge, inheritance cannot be as simple as has been implied.  There is no DNA test that can distinguish so-called homozygous dominant from hetereozygous.  In other words, by looking at a dog with a ridge, you do not know if the dog can produce ridgeless if mated to another dog or not.  It is hoped that by doing these two breedings, Dr. Hilbertz may be able to find more information so that eventually we can find a way to separate the heterozygous from the dominant dogs.
 
The other side of my investigation has to do with the presence of white, especially up the legs and the throat.  I realized when looking at my ridgeless dogs that they had, at most, small white dots on their chest, but no white patches, no white toes, and no white socks, even though ridged litter mates had excessive white.  My hypothesis is that by breeding away from white, we have increased the number of ridgeless dogs being born (a phenomenon I have noticed over the last 45 years).  I have been accumulating data from people all over the world and hope to eventually have a big enough sample to be statistically meaningful.
 
Don’t throw out the baby with the bathwater!  We may need those ridgeless dogs down the line!

 

Ann Chamberlain
Mazoe Ridgebacks

(Reproduction including excerpts, only with permission of the author)