Purina was the first to trumpet the results of an letter in the journal Nature reporting an in-depth study of the genetics of dogs vs. wolves. Their findings suggest that dogs have adapted their DNA to be able to digest and assimilate a high-starch diet. Purina is all about how wonderful corn is for dogs; they (and other big pet food makers) must be ecstatic about these findings.
- Gene: a sequence (area or region) of DNA that determines a particular characteristic, such as gender or coat color.
- Allele: a different version of a gene. An organism inherits two alleles of every gene, one from each parent.
- Genome: the entirety of hereditary information (DNA) of an organism. The dog’s genome has been sequenced (decoded); it contains about 19,000 genes.
- Genotype: the genetic makeup underlying a trait, cell, or individual.
- Phenotype: the physical manifestation of an organism’s DNA. This includes things like size, appearance, and heritable diseases. Phenotype is determined by genotype, but because an organism inherits DNA from both parents, the offspring’s phenotype will exhibit a mixture of the parents’ characteristics.
This seems to be a sound study using appropriate methods and analysis. For the first analysis, the researchers used pooled blood samples from 60 dogs of many breeds and 12 wolves from Europe and North America. They also examined the genotypes of 72 dogs of 38 breeds, and 19 wolves; as well as another sample of 507 dogs and 17 wolves. (It is not clear how much overlap there was among these groups.) With these numbers, the statistical power of the analyses should be good and the results reliable.
The authors also provide massive amounts of supplementary information describing all the technical data from the DNA analyses, as well as notes on the dog breeds used and original of the wolves. (One of the authors confirmed that DNA and serum samples came from wild wolves, whereas pancreas samples were obtained from captive wolves in zoos. This is important because there are known biochemical differences between wild and captive wolves.)
- Dogs had 4-30 copies of the gene for pancreatic B-amylase, wolves only 2. This suggests that dogs born with additional copies were more successful in the domestication process, and their genes were more likely to be passed to their offspring.
- The maltase pathway had one or two nucleic acid substitutions in two genes.
- A major glucose uptake gene had one nucleic acid substitution that was present in all dogs in the sub-sample, but no wolves.
Some DNA regions were “fixed” in the dog; these areas are present in every dog, and are no longer subject to change within the dog population.
Limitations of the study
There is broad agreement today that dogs are descended from wolves, period. No jackals, no coyotes, just wolves. Dog and wolf DNA are 99.8% identical, despite the major differences in looks and temperament.
Dog breeders, of course, try to minimize genetic diversity by breeding to a set standard of size, color, and other traits. However, it’s hard to selectively breed for one trait without inadvertently dragging other nearby genes along. Compounding the situation, many breeds suffer from the “Founder Effect” that occurs when the new breed is established with only a few individuals; or from a “bottleneck” that wipes out all but a few individuals of that breed. The result is a loss of genetic diversity, and amplification of traits from the original or remaining breeding stock–whether good or bad. These issues are at the root of why there are so many heritable diseases in today’s dogs, such as hip dysplasia and heart defects.
There are four breed groups based on clusters of alleles:
- dogs of Asian and African origin:
- herding dogs and sight hounds
- modern hunting dogs such as terriers, hounds and retrievers
- large mastiff-type dogs.
In addition, 14 breeds have been identified by DNA analysis as “ancient” or “basal.” All other breeds are thought to derive from them:
- Afghan Hound
- Alaskan Malamute
- Chow Chow
- Finnish Spitz
- New Guinea singing dog
- Shiba Inu
- Siberian Husky