Best friend's genome: dog's DNA sheds light on human genetics, too.

Looking at a pooch can reveal a lot about its owner, and now that includes the owner's genetics. A team headed by scientists in Massachusetts has announced the DNA sequence of a boxer named Tasha, a detailed comparison of the dog's genome with those of mice and people, and a study of genetic variation among dog breeds. The work will inform scientists' understanding of people as well as dogs, the researchers predict.

People domesticated the dog from the grey wolf from 15,000 to 100,000 years ago. In the past few hundred years, they have bred the species into roughly 400 varieties.

As people inbred dogs to develop special traits, the animals accumulated mutations that contribute to many diseases. Some, including cancers, blindness, and heart disease, progress in dogs much as they do in people. By knowing the dog genome, researchers may find disease genes affecting people, says Kerstin Lindblad-Toh of the Broad Institute in Cambridge, Mass.

The dog is the fifth mammal for which the genome has been worked out. "To understand the human and other mammalian genomes, we need to sequence a lot of them," Lindblad-Toh says.

In 2003, a different research group published 77 percent of a poodle's DNA sequence (SN: 9/27/03, p. 197). The multi-institution team that tackled Tasha's chromosomes set out to produce a nearly complete job. They determined 99 percent of the boxer's DNA sequence and report their findings in the Dec. 8 Nature.

The group also compared the dog genome with the genomes of people and mice. Past research analyzing the latter two species revealed critical DNA segments--making up about 5 percent of the human genome--that are nearly identical in the two species. The same segments showed up in the boxer's genome.

The three-way comparison affirms that these regions are "a core part of mammalian genomes," comments David Haussler of the University of California, Santa Cruz. "This is very exciting."

Only a minority of the critical DNA codes for proteins. Most of the sequences control the actions of protein-coding genes, scientists speculate.

The research team investigated where in the dog genome the critical noncoding DNA regions reside. They tend to cluster around genes involved in a mammal's development and growth, the team reports. It's possible that this noncoding DNA contains signals "that decide when [their neighboring] genes are switched on or off" says Lindblad-Toh.

The team conducted a third analysis for the new study, a comparison of the boxer's genome with small portions of DNA from 10 other dog breeds.

Across breeds, matched stretches of DNA tend to be short, in the range of tens of thousands of base pairs. This is because there has been plenty of time for genetic changes in the 9,000-or-so generations between all living dogs and their common ancestor, the grey wolf. But within dog breeds, matching stretches are much longer, in the range of millions of base pairs, because dogs within a breed have a common ancestor from just 30 to 90 generations ago.

This information should be helpful when designing studies to pinpoint the location of disease genes, notes Lindblad-Toh. Dogs within a breed provide larger DNA pieces for solving these genetic puzzles.