Dog DNA shows man's meddling

WASHINGTON - The genetic differences that distinguish a dachshund from a dobermann are so clear that a computer can tell breeds apart simply by looking at a dog's DNA, researchers have found.

A team scanning the genetic code of dogs for insight into human disease found a surprising 30 per cent 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 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, behaviour 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 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," she said.

"We're now looking at narrowing down similar regions of DNA to identify single genes that contribute to particular traits.

"There are hundreds of diseases out there, and many of them have counterparts in humans.

"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," Dr Ostrander said.

Her team sampled five unrelated dogs from each of 85 different American Kennel Club breeds.

- REUTERS