The genetic differences that distinguish a Dachshund from a Doberman are so clear
that a computer can tell breeds apart simply by looking at a dog's DNA, researchers
say. A team scanning the genetic code of dogs for insight into human disease found
a surprising 30 percent of genetic differences among dogs can be accounted for
by a few hundred years of intense inbreeding -- far more than the so-called racial
differences between humans.
They
were able to group 85 breeds of dog into four main genetic categories -- ancient
breeds such as Huskies and Pekingese, which may be the closest to their wolf ancestors;
hunting dogs such as Labradors; Mastiff-like breeds that include Rottweilers;
and sheepdogs, collies and other herders.
"Most
breeds have been artificially created by man," said graduate student Heidi
Parker at the Fred Hutchinson Cancer Research Centre in Washington, who worked
on the study published in Friday's issue of the journal Science. "Although
all are members of the same species, this selective breeding has resulted in amazing
variation between breeds with respect to weight, size, head shapes, coat, ear
shape, behaviours and diseases."
Howard
Hughes Medical Institute researcher Leonid Kruglyak said the number of tiny genetic
differences within a single species is not seen in any other species. For the
past 300 years, people have intensively and systematically inbred dogs to get
the traits they wanted -- tiny lapdogs such as toy poodles, guard dogs, racing
greyhounds and retrievers.
This
is such a short time by standards of evolution that scientists expect that each
distinctive trait has arisen from a small number of genes. This will make them
easier to track down, researcher Elaine Ostrander predicted. "There are more
than 400 breeds of dog, and each is an isolated breeding population," Ostrander
said in a statement. "We're now looking at narrowing down similar regions
of DNA to identify single genes that contribute to particular traits," Ostrander
said. "There are hundreds of diseases out there, and many of them have counterparts
in humans."
Doing
this within genetically similar breeds of dog should be easier than trying find
genes accounting for cancer or heart disease amid a background cacophony of genes
coding for traits such as fur colour or leg length. "Although there may be
just as many genes for a given disease in dogs as there are in humans, being able
to search for them in a single breed allows us to find the one or two genes responsible
for that disease in that population much more easily," Ostrander said. Her
team sampled five unrelated dogs from each of 85 different American Kennel Club
breeds.
"The
dogs of a particular breed are much more similar to one another than they are
to dogs of different breeds. These differences are so distinct that we could just
feed a dog's genetic pattern into the database, and the computer could match it
to a breed," Kruglyak said in a statement. This was a surprise. "It's
a much more striking difference than is seen among human populations that evolved
on different continents," he said.
So-called
ancient breeds such as the Pharaoh Hound and the Ibizan Hound, as well as the
Norwegian Elkhound, believed to be 5,000 years old, are no such thing, they also
found. "Our results indicate ... that these ... breeds have been recreated
in more recent times from combinations of other breeds," the researchers
wrote.
~
from Reuters Health and Science
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