By Julianna Kettlewell
BBC News Online science staff
Researchers have worked out how to identify a dog's breed just by looking at its DNA, Science magazine reports.
Dogs are a very useful model for studying diseases in humans
By examining the genes from 85 breeds of dog, the scientists have also been able to establish how they are related.
All the breeds fall into three "modern" categories - associated with guarding, herding and hunting - and one "ancient" group, that dates back to antiquity.
This detailed knowledge will help research into the causes of inherited diseases, which also affect people.
Dogs are a very useful model for studying genetic conditions in humans, because the two species share many of the same disorders.
If geneticists can identify which genes cause certain cancers in dogs, they should find it easier to locate the equivalent genes in humans.
But to make the most out of canine gene hunts, the authors, led by Elaine Ostrander, a geneticist at the Fred Hutchinson Cancer Research Center in Seattle, US, realised they had to establish the genetic differences among breeds.
They identified subtle differences in genetic signposts - called microsatellite loci - from 414 dogs belonging to 85 different breeds.
Professor Ostrander and her colleague Leonid Kruglyak then performed detailed statistical analyses of the data, to detect patterns that would reveal genetic differences among the breeds.
"The first major finding was that different breeds are quite genetically distinct," Professor Kruglyak told BBC News Online. "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 only formally isolated in the 19th Century, with the advent of breed clubs."
He added: "It's a much more striking difference than is seen among human populations that evolved on different continents."
As a parallel study, the researchers also looked at whether the differences would yield any general genetic classifications of dog breeds.
They found four breed clusters. Three were modern - probably dating back to the official formalisation of dog breeds in the 19th Century - but the fourth was out on an ancient limb.
The team were surprised to find such a diversity of breeds congregating in this group. The sharpei, Pekingese, shih tzu and Siberian husky all showed the closest genetic relationship to the wolf ancestor of dogs.
However, breeds that people commonly thought were very old - like the pharaoh hound, depicted on Egyptian tomb walls - turned out not to be.
The researchers think that, rather than being the "real thing", these dogs were recreated in the last couple of centuries.
The main reason why this study is so important is that it will help in the understanding of inherited diseases.
When geneticists are looking for the causes of a particular disease, they often find it very difficult.
The sharpei: Dogs take on all shapes and sizes
This is because there are not enough members of affected families, or isolated groups of people, to pin down the genetic "culprits". But with pedigree dogs this is less of a problem.
Pointers, for example, tend to suffer from lymphomas. And since there are an awful lot of pointers about - all sharing the same genetic disposition - there are plenty of subjects with which the researchers can work.
This study will help with grouping dogs according to their possible susceptibility to a particular disease.
"If we know a subset of breeds share a common lineage, then we can group them together when we're working on a particular disease," explained Professor Ostrander.
She added: "If I'm studying lymphoma, for example, and I know that a subset of Asian breeds shares a common lineage, I could group data from those breeds together, in order to gain statistical power."