Boxer bares all
Complete dog DNA sequence gives paws for thought.
Our faithful, four-legged friends may prove their use once again, now geneticists have the data to study canine quirks.
Today, researchers published the full genetic code of a 12-year-old boxer named Tasha. But she is not just another addition to the list of animals with completely sequenced genomes; Canis familiaris has a unique genetic background, thanks to us.
All domestic dogs are descended from grey wolves (C. lupus) that were tamed about 15,000 years ago. Over time, people have bred dogs to look and act in specific ways: think of the smush-faced pug or the friendly golden retriever.
We have created more than 400 dog breeds, each with its own traits, and its own genetic code. So it should be a lot easier to pin down the genetic roots of traits in dogs than in people, whose characteristics and genetic groupings are much less clear cut.
"This gives us a blueprint for how complex traits evolved in all breeds of dogs," says Elaine Ostrander of the National Human Genome Research Institute in Bethesda, Maryland, which helped fund the research.
Scientists had already made one stab at a dog genome, assembling 75% of the genetic code of a poodle named Shadow in 20031. Adding Tasha's complete code to the mix will make it easier to find the causes of genetic diseases, such as cancer, that affect both dogs and people.
Bark up the right tree
Dogs are less closely related to humans than other mammals, such as chimps, that have been completely sequenced. So scientists can use the dog genome to test their assumptions about the way mammals evolved.
The scientists involved in the effort, whose research appears in Nature on 8 December2, say Tasha's genome has already helped them to pinpoint a group of DNA sequences that do not code for specific genes, but are extremely similar among mice, humans and dogs.
The fact that these sequences are the same in all three animals indicates they could be crucial switches that control the activity of genes, the authors say. The discovery of such 'non-coding' regions, and the quest to find out what they do, is one of the most intriguing questions facing genomicists.
"These signals that decide when a gene will be turned on or off are extremely important," says Kerstin Lindblad-Toh, a geneticist at the Broad Institute in Cambridge, Massachusetts, which led the dog-genome analysis. "We're looking at the tip of the iceberg now, but when we get ten or twenty mammals we'll be able to crystallize this even further."
For now, the dog genome is fascinating in its own right. "Fifteen thousand years is a short time on the evolutionary scale," says evolutionary biologist Hans Ellegren of Uppsala University in Sweden. "To think that you could go from a wolf to a dachshund to a poodle or a German shepherd in that time is amazing."
- Kirkness E.F., et al. Science, 301. 1898 - 1903 (2003).
- Lindblad-Toh K., et al. Nature, 438. 803 - 819 (2005).
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