CHEVY CHASE, Md., May 21 /PRNewswire/ -- The first detailed genetic
comparison of purebred domestic dogs promises to rewrite the textbooks with
new information about breed classification and insights that may improve
canine health by boosting understanding of the more than 350 inherited
disorders, including cancer, heart disease, epilepsy, blindness and deafness,
which affect dogs.
In analyzing and carefully comparing the genetic information from dogs
representing 85 breeds, the researchers were surprised to discover previously
unappreciated relationships between existing breeds and new details that
suggest completely unexpected breeds to be among the most ancient descendents
of dogs' wolf-like ancestors.
The researchers, led by Elaine A. Ostrander and Howard Hughes Medical
Institute researcher Leonid Kruglyak, reported their findings in an article
published in the May 21, 2004, issue of the journal Science. Kruglyak and
Ostrander are at the Fred Hutchinson Cancer Research Center. Other co-authors
are from the University of Washington and the University of Missouri.
"In all the research on dogs, the question comes up over and over how
modern breeds are related to one another genetically," said Ostrander, whose
research has concentrated on using the power of genetics to understand canine
diseases. "The answer to this question has important implications for trying
to identify disease genes, because if we know a subset of breeds that share a
common lineage, then we know to group them together when we're working on a
particular disease. For example, if I'm studying lymphoma, and I know that a
subset of Asian breeds shares a common lineage, I could group data from those
breeds together, rather than considering them separately, in order to gain
more statistical power," she said.
For their analyses, the researchers obtained the help of the American
Kennel Club (AKC) and dog breeders across the country to acquire cheek-swab
DNA samples from purebred dogs at dog shows and directly from owners.
"While we only analyzed eighty-five breeds of the hundreds of recognized
breeds, those eighty-five included the great majority of popular breeds," said
Ostrander. "Just the top 20 breeds, which include the Labrador Retriever, the
German Shepherd and the Dachshund, account for about seventy percent of all
AKC registrations."
To compare the breeds, the researchers analyzed the DNA samples from the
cheek-swabs for subtle differences in genetic signposts, called microsatellite
loci, among the dogs. The analysis covered 414 dogs from the 85 breeds
studied.
Kruglyak and his colleagues performed detailed statistical analyses of the
data to detect patterns that would reveal genetic differences among the
breeds. The researchers also sought to determine whether the genetic
differences they found would yield any general genetic classifications of dog
breeds.
"The first major finding was that the different breeds are quite
genetically distinct," said Kruglyak. "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.
"This finding was a bit surprising because most of the breeds are quite
recent and were formally genetically isolated only in the nineteenth century,
with the advent of breed clubs and breed standards," said Kruglyak. "It's a
much more striking difference than is seen among human populations that
evolved on different continents," he said.
The genetic comparisons also enabled the researchers to cluster many
breeds according to shared lineages. The researchers found four such clusters,
in particular the separation of breeds that are more ancient from those that
probably dated from the 19th century at the time when breeds were formally
established.
The researchers said they were surprised that the cluster containing the
more ancient breeds of Asian and African origin included such a diversity of
breeds -- such as the Basenji, Saluki, Afghan, Lhasa Apso, Pekingese, Sharpei,
Shih Tzu, Akita, Alaskan Malamute, Siberian Husky and Samoyed. All of these
breeds showed the closest genetic relationship to the wolf ancestors of dogs,
said the researchers.
Noticeably absent from this ancient cluster were several breeds long
regarded as the most ancient by breeders, including the Pharaoh Hound and the
Ibizan Hound -- depicted on Egyptian tomb walls. The researchers said their
analysis indicated that the modern representatives of these breeds were
recreated in more recent times from combinations of other breeds. The
researchers also found genetic evidence for a recent origin of the Norwegian
Elkhound, believed to be of ancient Scandinavian origin.
Another group of breeds that clustered genetically included the mastiff-
type dogs such as the Bull Mastiff, Bulldog and the Rottweiler. A third group
included the herding dogs, and a fourth included the terriers and scent
hounds.
Further studies will include more detailed analyses to focus on
differences within breeds and between related breeds. Such insights may enable
even deeper insights into the origins of inherited diseases to which those
breeds are susceptible, said the researchers.
The Howard Hughes Medical Institute was established in 1953 by the
aviator-industrialist. HHMI's principal mission is conducting basic biomedical
research, which it carries out in collaboration with more than 66
universities, medical centers and other research institutions throughout the
United States. Its more than 300 investigators, along with a scientific staff
of more than 3,000, work at these institutions in Hughes laboratories. The
Institute also has a philanthropic grants program which is strengthening
science education and training, from elementary school through graduate and
medical school. It also supports the work of biomedical researchers in many
countries around the globe.
HHMI is one of the largest philanthropies in the world, with an endowment
of more than $12 billion. Its headquarters are located in Chevy Chase,
Maryland, just outside Washington, D.C.
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SOURCE Howard Hughes Medical Institute
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CONTACT:
Jim Keeley of Howard Hughes Medical
Institute, Communications, +1-301-215-8858
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