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Dog DNA research re-writes the book

NEW RESEARCH into the canine genome threatens to re-write a huge chunk of our received knowledge of diverse canine breeds including their behavioural traits and even their history and development. The genetic signatures that produce breeds of dog as diverse as the Chihuahua and Rottweiler have been mapped by American scientists in a study with important implications for both canine and human health.

A detailed comparison of the genomes of 85 breeds has uncovered their unique DNA profiles, which explain the vast physical and even behavioural differences between the breeds.
The findings promise to uncover the genes responsible for traits such as aggression, herding, retrieving and body size, as well as those that cause more than 300 inherited canine diseases. This would enable breeders to eliminate painful hereditary disorders such as Hip dysplasia by choosing only the healthiest dogs for breeding, although great strides have already been made in this direction thanks to the AHT/KC’s own genetic screening programmes.

Genetic screening could also allow more targeted selection of positive traits, such as a placid temperament for guide dogs. This area of genetic research, however, is bound to prove contentious, as campaigners against Breed Specific Legislation have argued – and even proved legally and scientifically – that one breed cannot be ‘genetically more aggressive’ than another.

Human medicine will benefit as well, as at least half the inherited conditions that affect dogs resemble human diseases. A better understanding of the canine genome will thus help scientists to trace the genetic origins of cancer and other life-threatening disorders inhuman beings.

The study, led by researchers at the Fred Hutchinson Cancer Research Centre in Seattle, USA has also shed important light on the evolution of modern dog breeds. It shows that each breed belongs to one of four clear genetic lineages, reflecting the way that it has been isolated and selectively mated by human beings over many centuries.

The most ancient group includes dogs of African, Asian and Arctic origin such as the Siberian husky, Alaskan malamute, Afghan hound and Pekingese. These show the closest genetic resemblance to the grey wolf, from which dogs were domesticated in Asia about 15,000 years ago.

The other genetic groups are the mastiff-like dogs, including the Rottweiler, Bulldog, Boxer and German shepherd; the herding dogs, including the Collie and Old English Sheepdog; and the various hunting dogs, including the Labrador, Golden Retriever, Terriers, Beagle, Bloodhound and Dachshund.

In the research, details of which are published in the latest edition of the journal Science, a team headed by Elaine Ostrander, Leonid Kruglyak and Heidi Parker based at the Fred Hutchinson Cancer Research Center in Washington took cheek swabs from 414 purebred dogs of 85 breeds to obtain samples of their DNA. These were examined using a technique known as microsatellite analysis to draw up distinct signatures for each breed.

Distinct

These proved so reliable that in a blind test the scientists assigned 99 per cent of dogs to the correct breed by looking at their genetic profile. Only four out of the 414 dogs were assigned wrongly and then to a very closely related breed.

"The first major finding was that the different breeds are quite genetically distinct," Dr Kruglyak said. "The dogs of a particular breed are much more similar to one another than they are to 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."
While scientists have long understood that genes caused the differences between breeds, the team was amazed to be able to detect them so easily: it is impossible to distinguish between human races in this fashion.

"This finding was a bit surprising because most of the breeds are quite recent and were formally genetically isolated only in the 19th century, with the advent of breed clubs and breed standards," Dr Kruglyak said. "It’s a much more striking difference than is seen among human populations that evolved on different continents."

The way in which dogs, which all belonging to the same species, have so many distinct inbred traits make them an ideal animal model for investigating genetic origins of human disease.

Individual genes stand out much more obviously in populations closely related to one another, which is why genetic scientists often study relatively isolated human societies, such as that of Iceland.

"Most dog breeds have been artificially created by man," added graduate student Heidi Parker. "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."

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 to 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.

The researchers also claim that some 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 not as ancient as they seem and were "recreated in more recent times from combinations of other breeds."