Dog genome unveiled

JOHN WHITFIELD

Shadow has 18,473 genes with human equivalents. © C. Venter

Shadow is getting on a bit. At nine years old, his black coat is turning grey, and his favourite pastime is eating.

But this ordinary poodle is guaranteed a place in the annals of science. The dog is the latest animal to have its genome sequenced. Shadow belongs to Craig Venter, the researcher whose privately funded project sequenced the human genome using his own DNA.

Shadow's sequence will aid the quest to identify human genes and to understand diseases such as cancer, epilepsy, narcolepsy and obsessive-compulsive disorder. It should also help to breed healthier dogs and track canine evolution.

The new sequence reveals that 18,473 dog genes have human equivalents. This already surpasses the 18,311 known from the mouse sequence. The team also found genes related to a dog's life: they have many more that are linked to smell than we do.

The freely available sequence is less complete than those of mouse and human. "We have a lot of fragments," says Ewen Kirkness of The Institute for Genomic Research in Rockville, Maryland, who led the project. About 2 million fragments, in fact, covering 80% of Shadow's genome.

A rough survey can still provide a lot of information, says genome researcher William Murphy of the National Cancer Institute in Frederick, Maryland. "Given the relatively low coverage, the results are pretty good," he says. The quick-and-dirty technique could be extended to other species that don't merit a full genome project.

Meanwhile, a US government-funded venture is working on a detailed dog genome, from a boxer called Tasha. This is expected to be completed late this year or early next. Boxers are among the least genetically variable breeds, and so likely to give reliable reference sequence.

Dogs have 2.4 billion DNA letters, compared with our 2.9 billion, and 39 pairs of chromosomes to our 23. Different breeds are more than 99% identical.

Dog trials

"Most human diseases have canine counterparts, and dogs are closer to humans in size, lifestyle and lifespan than rodents," says dog geneticist Gregory Acland of Cornell University in Ithaca, New York. He has already used Shadow's sequence in his work on eye disease.

There are more than 350 known genetic dog diseases, surpassing all animals save humans. About 10% of Irish setters, for example, carry a gene for an immune disease. DNA testing has allowed breeders to avoid mating carriers. The genome will accelerate the search for such genes, says Jeff Sampson, chief geneticist with the UK Kennel Club.

Others are using genetics to work out relations between dogs. "The genome might help to reveal how breeds have developed over the centuries," says Sampson. Comparisons of the tiny differences between breeds might explain why collies are so good at herding, or what gives bloodhounds their acute sense of smell.

1. Kirkness, E. F. et al. The dog genome: survey sequencing and comparative analysis. Science, 301, 1898 - 1903, (2003). |Homepage|