How can a Chihuahua and a Doberman belong to the same species? A detailed analysis of the dog genome answers these questions and will also shed light on human health and biology, scientists said on Wednesday.

A U.S. government-funded study of the complete genetic map of an inbred boxer named Tasha not only helps explain how poodles differ from jackals, but also might offer insights into bone cancer, blindness and epilepsy, the researchers said.

“It’s going to make the identification of many disease genes 50 times easier,” Dr Eric Lander, a gene expert at the Broad Institute at the Massachusetts Institute of Technology and Harvard University who helped coordinate the study, told a news conference.

“It ought to be possible in the next three to four years to identify a gene for bone cancer in dogs.”

Writing in the science journal Nature, the researchers at 15 institutions described how they compared the genetic blueprint of the boxer with 10 other breeds. They also compared the dog genome to the already-completed maps of human genes, mice, rats and chimpanzees.

The team, led by the Broad Institute’s Kerstin Lindblad-Toh, sequenced the 2.4 billion letters of Tasha’s DNA, representing 39 pairs of chromosomes. There lies one big difference between dogs and people - human genes are found on just 23 pairs of chromosomes.

The researchers also compiled a catalog of 2.5 million single-nucleotide polymorphisms - one-letter changes in the genetic code - that differ among the 10 breeds of dogs studied.

The genes that make some dogs big and others little, that give some dogs long snouts and others pushed-in faces, and that predispose some dogs to certain diseases provide a convenient laboratory for studying biology, medicine and evolution.

“The hundreds of years of careful inbreeding to produce the various breeds have delivered a geneticist’s dream model for human genetic disease,” Hans Ellegren of Uppsala University in Sweden wrote in a commentary.

In 2003, teams at The Institute for Genomic Research and genome entrepreneur Craig Venter’s Center for the Advancement of Genomics in Rockville, Maryland, published a genetic map of Venter’s pet poodle.

But the U.S. government-funded team said their study was more complete and systematic.

“Until now we only had little shreds of the dog genome. We now have the entire book from end to end, ready to read,” Lander said.

The researchers, who staged their news conference at a dog show in Massachusetts, were clearly fans of man’s best friend.

“The incredible physical and behavioral diversity of dogs - from Chihuahua to Great Danes - is encoded in their genomes. It can uniquely help us understand embryonic development, neurobiology, human disease and the basis of evolution,” Lander said.

Elaine Ostrander, chief of cancer genetics at the National Human Genome Research Institute, said dog genetics could help narrow down the search for human disease genes.

“The leading causes of death in dogs are a variety of cancers, and many of them are very similar biologically to human cancers,” Ostrander said.

“They breathe the same air, drink the same water and walk across the same lawns that we do,” added Dr. Matthew Breen, associate professor of genomics at North Carolina State University, who worked on the project.

“Cancers that dogs get are exactly the same as the cancers that we get.”