Human, Dog Genomes Similar, Study Finds

Stefan Lovgren
for National Geographic News
September 25, 2003
Scientists have completed a rough sketch of the canine genome. The results may explain why dogs are humans' best friend: Their genes are similar.

The successful sequencing of the dog genome sheds light on the structure and function of the human genome, and could help researchers better understand diseases that affect both humans and dogs.

"Dogs suffer from more than 350 genetic disorders, many of which resemble human conditions," said Ewen Kirkness, a molecular biologist at the Institute for Genomic Research in Rockville, Maryland, who led the research. "The genes responsible for these are probably constant to humans and dogs."

Kirkness and his team covered the genome of a standard poodle one and a half times. That means the amount of DNA sequence they generated is one and a half times the length of the genome. In contrast, a high-level method recently used to sequence the human and mice genomes covered those genomes eight times.

While the shallow sequencing method does not give as complete a picture of the genome as the high-level sequencing method, it is far less expensive. Kirkness believes his technique will allow scientists to sequence genomes of species they could otherwise not afford to study.

"We can learn a lot more about mammalian evolution on a molecular level by applying this technique to a wider diversity of species," said Kirkness. "Species like whales and elephants can tell us a lot. But from a purely financial standpoint, they will [not] be candidates for complete sequencing [anytime soon]."

The research, which was started in 2001, is described in tomorrow's issue of the journal Science.

Dogs and Humans

The rough sequencing of the dog genome is the latest advance in the field of comparative genomics. To date, researchers have sequenced the human, mouse, rat, worm, fly, and fungi genomes.

The sequencing indicates that dog and human genomes are more similar to each other than either is to the mouse, though it appears the dog lineage diverged first from the common ancestor.

Dogs are important to researchers because they can be used as biomedical models for understanding human diseases. The top ten diseases among purebred dogs include several that afflict humans, including cancer, epilepsy, heart disease, allergy, retinal disease and cataracts.

The dog has also been studied by pharmaceutical companies and universities as an important physiological model and has aided the development of bone marrow transplant techniques.

Scientists hope the completed sequence of the canine genome could eradicate progressive retinal atrophy (PRA), an inherited disease that causes blindness in dogs. It could also help researchers determine which gene causes a blinding disorder similar to PRA that exists in humans, called retinitis pigmentosa.

Completing the Picture

The technique used by Kirkness to sequence the poodle's genome, one and a half coverage of the genome, gave him only 80 percent of the sequence. Compare that to a coverage of eight times—the location of every DNA letter is determined an average of eight times—which completes 95 to 98 percent of the sequencing.

But Kirkness says the more complete sequencing of the human genome helps him to complete the picture of the dog genome.

"We ended up with a genome that is many more fragments than if we had a more complete sequence," said Kirkness. "If we were to look at the fragments in isolation, they would be hard to interpret. But we can use the human genome as a platform on which we can lay the fragments, and use the interpretation of the human sequence to understand what the fragments are."

Meanwhile, in a separate project at the Whitehead Institute for Biomedical Research in Cambridge, Massachusetts, scientists are working on the high-level sequencing of a female boxer dog genome.

The boxer is one of the breeds with the least amount of variation in its genome and therefore is likely to give an easily assembled genome sequence.

That sequencing is scheduled for completion in June 2004. It will then be compared to small amounts of sequence from 10 to 20 other breeds, including the beagle, to study genetic variation within the canine species.

Researchers at Whitehead have also sequenced the chimpanzee genome, though the results have not yet been published. Since the chimp genome differs from the human genome by only about 1.4 percent, it could greatly expand understanding of human disease, human evolution, and genetic selection.

But the complete genome sequencing of a species can cost U.S. $50 million. Kirkness believes his cheaper approach provides an attractive alternative.

"I think [our research] will spark debate on how to move forward for genome sequencing," he said. "I hope it will demonstrate that a lower level sequencing is good. At present, there are very few mammalian species that are being earmarked for sequencing, purely because of the expense." Resources on Dogs

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A Love Story: Our Bond With Dogs from National Geographic magazine
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Veterans: Dogs of War Deserve a Memorial
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Crisis-Response Dogs Offer Comfort After Tragedy
Dogs Are "True Heroes" of Iditarod, Race Champ Says
Brooklyn Dog a Rising Star in New York Art Scene
Canine Companions May Help Kids Learn to Read
U.S. Beagle Brigade is First Defense Against Alien Species

Science and Dogs
Scientists Start Deciphering Dog Genome
Human Gestures Fed Dogs' Domestication
Animal Acupuncture: More Pets Get the Point
National Geographic magazine's "Wolf to Woof: The Evolution of Dogs"

News and Features About Other Canids
Eco-Terrorism Blamed for Tasmania Red Fox Release
Coyotes Now at Home in Eastern U.S.
Rare-Dog Search Meets With Success, Then Tragedy
Hi-Tech Tracking Tool Tested in Wolf Recovery Efforts
Scandinavian Wolves on Road to Recovery, Study Says
Most-Endangered Wolves May Be Saved By Vaccine
Is U.S. Safe From Foxhunting Debate?

Related Lesson Plans:
Use National Geographic News articles on dogs in your classroom with these Xpeditions lesson plans.
Lesson Plan: Little Red Riding Hood Meets—A Golden Retriever?
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Lesson Plan: The Human Role in Dog Evolution

More About Animals
National Geographic Animals and Nature Guide

Other Web Sites
List of Dog Breeds (American Kennel Club)

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