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Science unravels dog genetics

Researcher probes diversity of canine breeds

The Rocky

Published June 30, 2008 at 11:42 a.m.
Updated June 30, 2008 at 11:42 a.m.

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Pug

Pug

Irish Wolfhound

Irish Wolfhound

American Staffordshire Terrier

American Staffordshire Terrier

American Pit Bull

American Pit Bull

Top, an Ibiza Hound. Bottom, a Mexican Hairless.

Top, an Ibiza Hound. Bottom, a Mexican Hairless.

Alaskan Husky

Alaskan Husky

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Scientists have uncovered some genetic secrets to why an Irish wolfhound can be so huge, a Chihuahua so small, a retriever so eager to retrieve — when all are members of the same species.

Twenty millennia ago, there were only wolves, not dogs.

Now there are Bluetick Coonhounds, miniature poodles, Great Danes and dachshunds, among 350 other breeds of dogs.

How could so much diversity have happened in so short a time, given what scientists know about evolution?

"Twenty thousand years ago, all of these traits were present in wolves, but they were hidden," Paul G. Jones, a Mars Veterinary genetics researcher at the Waltham Centre for Pet Nutrition in England, said.

While the wolves didn't vary in size much, some of the wolves were more timid than others, some were vicious, some wanted nothing to do with humans, others would creep close to human settlements.

Of the ones that showed an affinity toward humans, some proved capable of hunting, some of herding, some of burrowing under enclosures, some of playing with the kids.

Somewhere in all that cross-breeding of wolves, specific genes learned how to be more active and variant.

Keep breeding a small wolf to a small wolf often enough, and before your great-great-great grandchildren know it you have a dog that can burrow under walls and keep the vermin away from the grain.

Keep breeding a large wolf to a large wolf and eventually you've got a dog the size of an Irish wolfhound or a mastiff.

By slowly pulling different aspects of wolves into dogs, "we got collies, Labradors, beagles ..." Jones said.

Jones is co-author of a study appearing in this week's edition of the scholarly journal Genetics, in which researchers from Utah, California, and the United Kingdom, studied simple genetic markers to find places in the dog genome that correlate with unique and unusual breed traits.

Researchers zeroed in on the hots spots, to isolate genes that could contribute to differences in size, color, weight, behavior and propensity for disease.

They knew going in that dogs vary in size, shape, color, coat length and behavior more than any other animal.

The key to the breakthrough is an expanding data base that now includes DNA from 25,000 dogs, kept by Mars Veterinary, Jones said. Some 13,000 samples were examined for this study.

With that many samples, scientists delineated the ranges — from large to tiny, from timid to bold, from friendly to mean, herding or pointing ability — "to hone in on where in the dog genome these traits actually lie," he said.

All of the diversity in the dog kingdom "wouldn't have happened by natural evolution," he said. "We've been breeding dogs for at least 15,000 years."

No one can imagine a Chihuahua surviving in the wild, or in any kind of cold climate, but it is a great pet in Mexico, and once was used in religious sacrifices among the Aztecs. It may have originated in Mexico, or may have evolved from Asian dogs bred to satisfy the emperors' tastes for smallness and tender meat.

The hope is that the expanded knowledge about dog breeds will help develop medicines to improve the health of the canines — and possibly of their human cousins, as well.

Pit bulls were bred as fighting dogs in England, and ever since bull baiting was banned there in 1835, they've been fighting against a negative image. The American Kennel Club says they make good house pets, and they managed to win some good publicity by being the symbol of U.S. WWI fighting forces and the mascot of the kids in the Our Gang serials. But they also get in the news for attacking children and adults.

Critics would say the problem isn't the pit bull, but the owners who are attracted to a breed with a propensity for violence in their ancestral past.

One more thing about pit bulls — officially, Staffordshire bull terriers: they very rarely get breast cancer, even though other breeds of dog get it commonly.

By examining the sequence in the breast cancer gene in pit bulls, and contrasting it with corresponding genes in other breeds and in humans, scientists could come up with a medication that helps fight breast cancer.

"We're looking for breeds with a propensity for different conditions," Jones said.

The Mars company, a pet nutrition and health firm, established the DNA data base as a way to understand where dog nutrition should be in the next 45 or 50 years and to look at the unique needs of different breeds, Jones said.

Samples were collected in North America, Europe and Asia.

In the United Kingdom, clubs supplied the names of dog owners, and sample packs were mailed to 46,000 breeders.

In the United States, veterinarians at dog shows sampled the dogs. "There were lines of people lining up before and after showing their dogs," Jones said. "So many dog breeders and dog owners care so much about health and genetics."

The database-by-breed was possible because early humans bred dogs for highly specialized jobs thousands of years ago. Much of the diversity we see today already had been established by the time the earliest writing tools were able to record it.

Once the breeds were firmly established — Alaskan huskies for mushing, German Shepherds for herding — the circle was closed and only dogs within that breed were allowed to mate, Jones noted.

"That created an island effect," and within those clearly separated islands were both useful traits and the propensity for diseases and physical problems unique to the breed, he said.

"Humans have pulled the maximum flexibility out of the dog gene," added Jones. "Whether they've wanted a dog to protect the grain from vermin or for hunting or herding, the dog has always answered."

Comments

  • June 30, 2008

    1:18 p.m.

    Suggest removal

    my3pugs writes:

    My dogs ancestors were among those that were attracted to humans initially because the fools would feed them. In return, they ARE friendly, just wish the snored a little more quietly.

  • June 30, 2008

    2:32 p.m.

    Suggest removal

    CyberHostage writes:

    I envision a tropical paradise where genetically engineered canines chase Jeff Goldblum and Laura Dern around.