Dog genome completed

US scientists have unveiled a completed version of an entire dog genome, that of a 12-year old Boxer named Tasha. The researchers, from a publicly-funded consortium based at the Broad Institute in Cambridge, Massachusetts, have published their findings in the journal Nature. They also sequenced smaller parts of the genome from other breeds, including the German shepherd, beagle and greyhound, as well as a related wolf and coyote species. A rough draft of the dog genome was published in September 2003, when 80 per cent of the genetic code of Craig Venter's poodle Shadow was assembled. The complete code of Tasha will, scientists hope, make it easier to find the causes of genetic diseases in both dogs and humans.

When Shadow's genetic code was unveiled, the comparison between the human and dog genomes showed that 18,473 of the estimated 24,567 dog genes have human equivalents, compared to 18,311 genes shared between mice and humans. The dog genome sequence is made up of around 2.4 billion DNA base-pairs, or 'letters', whereas humans have around 2.9 billion. These results showed that humans are much closer to dogs in evolutionary terms than they are to mice. The researchers said that their results would be useful for dog owners and breeders, as they would enable the identification of genes involved in over 350 dog diseases. Studying genetic variation in dogs could also reveal why some breeds are much better at hearing, or what gives others their acute sense of smell. Dog geneticist Gregory Acland, of Cornell University, pointed out that most human diseases have human counterparts, and that 'dogs are closer to humans in size, lifestyle and lifespan than rodents'.

All breeds of domestic dog share a common wolf ancestor, tamed thousands of years ago, so all dog genomes are 99.85 per cent similar. This means that 'a dog is a dog in a genomic sense', says Kerstin Lindblad-Toh, the lead researcher in the new study. The scientists hope that revealing the full genome of a new breed will make it easier to identify the genetic basis for traits shared between different types of dog. A Boxer was chosen because it is highly inbred. In addition, because dogs are less closely related to humans than other animals whose genomes have been sequenced, such as the chimpanzee - whose complete genome was revealed in September this year - the genome can be used to test theories about how mammals evolved. The fact that the dog has evolved so much in such a relatively short time is of great interest to scientists. 'Fifteen thousand years is a short time on the evolutionary scale', said Hans Ellegren of Uppsala University, Sweden, adding: 'To think that you could go from a wolf to a dachshund to a poodle or a German shepherd in that time is amazing'.

The researchers who sequenced Tasha's genome say the work has already enabled them to locate a group of DNA sequences that appear to be similar in humans, dogs and mice, although they do not code for specific genes. This means, say the scientists, that they might be crucial 'switches' - or areas of the genome that control the activity of the genes. The researchers have also identified around 2.5 million DNA variations scattered throughout the dog genome, which will help pin down genes involved in diseases such as heart disease, cancer, epilepsy and deafness.