Join Date: Aug 2006
Location: Lake Gaston, N.C.
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Yes, they are the same. I don't think a straight legged dog is considered to be a dwarf. There are short legged breeds, like the Dachshund, some Bulldogs, and Corgi, but their Standards call for short straight legs. Of course, there are still individuals of those that get the bowed legs. Some people say that these are Dwarf, or CD, breeds, but this is not correct. There is no "CD breed".
Chondrodysplasia was a term actually coined by the Malamute folks back in the '70s. Pam was breeding Malamutes for a short time back in the '70s when I met her. I remember one breeder saying that CD legs made them a better pet because they didn't want to run as much, which of course I was horrified by.
The Ostrander study found that all CD, or dwarf, dogs have retrogenes of the FGF4 gene. The Ostrander group was looking for the location to aid in finding out about human dwarfism, and the dog genome made it simple to find. They went to dog shows and took DNA from all the short legged breeds. I don't know that the Ostrander group isolated the gene for short legs. Vetgen is working on a genetic test for it, but it's not done yet.
The Texas A&M study, that self-proclaimed experts say was useless, and others read their own results into it, found that short legged dogs had something like 113 genes that were different on one chromosome, than dogs with equal proportions. The chromosome that the Ostrander group found the FGF4 retrogene, was the same chromosome that TAMU found the 113 different genes on. Equal proportions are legs that were at least as long (in Havanese the same) from the floor to elbow, as from elbow to top of withers. The definition of a short legged dog is one that is shorter from floor to elbow, than elbow to withers. My theory is that short legs are already a retrogene of the FGF4 gene, and CD is a retrogene of the retrogene, by no one has worked on that theory yet.
The Havanese Standard has always called for equal proportions, until someone also added "short legged dog" into the description. This really confused things because when one judge was asked why he picked a particular dog, he said, "because it was the only dog in the ring with short legs". So few people really understand conformation, and leave what is a correct dog up to the Judges.
In any case, it's one of those genetic things with "incomplete penetrance". That a fancy phrase used by geneticists that means even though an individual carries the genes that cause something, they might not exhibit the problem 100% of the time. This is fortunately the case with many other health issues, including the ones that have been found in the 113 genes. It seems that every week another ailment is found to be caused by retrogenes. A retrogene is one that gets put a little bit in the wrong order when an offsprings DNA chain gets out of order in transfer from it's parents.
Last edited by Tom King; 08-13-2011 at 07:53 AM.