Man’s best friend, in this case a male poodle, is genetically more similar to humans than is the mouse, a more commonly used laboratory animal, according to researchers who have completed the first rough draft sequence of the genes of a dog.
Since the start in recent years of intense genetic sequencing, more than 150 species, mostly bacteria, have been completed, but the study appearing this week in the journal Science is the first for a companion animal.
A standard size poodle named Shadow, the family pet of gene researcher J. Craig Venter, provided the specimen that researchers at The Institute for Genomic Research and the Center for Advancement of Genomics used to sequence the canine genes.
“Shadow is now one of history’s most valuable dogs,” said Venter, founder of the both institutions and leader of one of the two teams that first sequenced the human genome.
The rough draft shows dogs have about 2.4 billion base pairs of DNA, or about half a billion fewer than humans.
Boon to medical research
Ewen F. Kirkness of the institute for Genomic Research, the first author of the study, said that genetic sequence is important for medical research because dogs share about 360 of the same genetic disorders that are known in humans.
Dogs, he said, are second only to humans in the thoroughness of medical understanding and research.
Also, Kirkness said the dog is much more genetically similar to humans than is the mouse, even though mice and humans are closer together on the tree of evolution.
All mammals, at one point, had a common ancestor. But dogs are known to have diverged toward an independent species about 95 million years ago. The mouse and humans both diverged about 87 million years ago, making mice closer to humans in time.
“We are much closer to the dog than to the mouse in terms of our gene content and structure,” said Venter. “But if you do the evolutionary tree, we are on the same linage as the mouse. The mouse is evolving at a much faster rate.”
The researchers achieved what is called 1.5 X coverage of the dog genome. This means many DNA fragments remain and the results are less accurate than the completed sequences of some other species. For instance, the mouse has been sequenced to a 8 X coverage, which is considered ideal and essentially complete.
But Venter said because of the genetic sequences already completed for other species, particularly the human and the mouse, his team was able through comparison to quickly identify genes and gene regulatory elements in the dog genome that match those in other mammals.
Using this technique from species to species will enable researchers to more quickly and at less cost identify the genetic source of many human disorders, he said.
Venter said his labs can now do three other mammal species, probably the whale, elephant and dolphin, for what it would have cost to carry the dog genome to an 8 X fidelity.
William J. Murphy, a researcher at the Laboratory of Genomic Diversity at the National Cancer Institute, said the major contribution of the study by Venter and his co-authors is that it shows that a low fidelity sequence of mammal genes can be very useful and more quickly advance human genetic studies.
“We can do more species at lower cost and still annotate (identify) elements of the human genome with equal power,” he said.
A more complete genetic sequencing of the dog is being funded at another lab by the National Institutes of Health, Murphy said, and is expected to be finished next year.
With the dog completed, can the cat be far behind? Murphy said his lab has proposed sequencing the feline genome. The chicken genome is expected to be finished this year and gene sequencing has been proposed for the pig and the cow, he said.