Researchers delight in dogs' diversity

Dogs carry genetic codes linked to illnesses that are similar to human diseases.
SCRIPPS HOWARD
A kennel's worth of genetic information about dogs released Wednesday has researchers of both canine and human diseases drooling at the prospect of a new chapter in the 100,000-year-old relationship between man and dog.
With hundreds of breeds representing the greatest biological diversity of any mammal, dogs not only offer an incredible array of physical and behavioral traits, they also carry genetic codes linked to diseases that match many human ills.
So a set of publications that include a detailed gene map for a boxer named Tasha, a comparison of her genes with those of a poodle named Shadow, and then with snippets of genes from nine more breeds, plus four wolves and a coyote, along with other analyses of genes and specific traits, all could add up to healthier dogs -- and their humans.
"Of the more than 5,500 [species of] mammals living today, dogs are arguably the most remarkable," said Eric Lander, a professor of biology and director of the Broad Institute of MIT and Harvard University who is senior author of the gene map published today in the journal Nature.
"The incredible physical and behavioral diversity of dogs, from Chihuahuas to Great Danes, is encoded in their genomes. It can uniquely help us understand embryonic development, neurobiology, human disease and the basis of evolution."
Effects of selective breeding
Humans domesticated dogs from wolves as far back as 100,000 years ago, but most of the roughly 400 distinct modern dog breeds can be traced to selective breeding going back several hundred years.
While breeders seek to preserve certain physical or behavioral traits, such as long coats or herding instinct, breeding also predisposes many dogs to genetic disorders that include heart disease, cancer, blindness, cataracts, epilepsy, hip dysplasia and deafness.
"The leading causes of death in dogs are a variety of cancers, and many of them are very similar biologically to human cancers," said Elaine Ostrander, chief of the Cancer Genetics Branch of the National Human Genome Research Institute and a co-author of the Nature study.
"Using the dog-genome sequence in combination with the human-genome sequence will help researchers to narrow their search for many more of the genetic contributors underlying cancer and other major diseases."
DNA differences
In the December issue of the journal Genome Research, scientists reported that there were 10,562 differences between the boxer and the poodle in short stretches of DNA that separate and regulate genes.
The researchers from the nonprofit Institute for Genomic Research in Rockville, Md., say that, based on the comparisons with similar DNA stretches in the other dog and wolf breeds, there are about 20,000 such differences in the entire dog population. "This may have a profound impact on gene expression differences and disease determination in dogs," said Ewen Kirkness, lead investigator for the project.
Gene maps have already started to yield specifics about dog diseases for some breeds, such as a muscle-wasting disease in Labrador retrievers. The American Kennel Club's Canine Health Foundation, which has contributed $2 million, blood samples and other technical support to dog-DNA efforts, hopes to eventually be able to screen dogs for genes known to cause disease and disability before they're bred.
Human research
The dog research also helps reveal the evolutionary pedigree of human genes.
Humans and hounds branched off about 95 million years ago, yet nearly all of the estimated 19,300 dog genes correspond to similar genes in humans. But dog cells break their DNA into 78 chromosomes, compared with 46 in human cells.
As scientists compare the gene maps of the two species, they're beginning to wonder if humans really have 23,000 or more genes, as once thought, or if some genes really are just "junk DNA" that don't actually have any function.
Moreover, in comparing human, dog and mouse gene maps, researchers found that about 5 percent of the genes in all three species have gone virtually unchanged over the past 100 million years, and that preserved DNA is clustered in genes that regulate proteins involved in development.