The researchers were able to conduct this comparison between American, European, and East Asian dogs thanks to a large data set of mitochondrial DNA sequenced from thousands of dogs. They were also able to compare their modern sequences with 19 ancient dog genomes taken from remains found in Bolivia, Peru, Mexico, and Alaska.
Mitochondrial DNA comes from structures in cells called mitochondria, which function like battery packs, supplying energy for the cell's activities. They are inherited only from an organism's mother.
It's easier to compare genomes between individuals using mitochondrial DNA than using DNA from a cell's nucleus, explained Boyko, a National Geographic grantee.
Nuclear DNA comes from both the mother and the father, and the copies can swap pieces with each other in a process called recombination. This makes for an amazing variety of looks in the offspring, but creates enormous headaches for scientists trying to track down a population's origins.
"It gets complicated really quickly," Boyko said.
Buildup
The sheer scope of the canine genetic analysis is impressive, he said. Not only did the team look at breeds from the Old and New World, but they also looked at stray dogs in the Americas.
One hitch is the fact that the researchers were limited in the number of genetic markers they examined, Boyko said. The authors acknowledged as much in the paper, he added, and it shouldn't take anything away from the study.
Indeed, co-author Savolainen said he plans on looking at nuclear DNA in these dog populations to get a sense of how big the founding population might have been, and to pin down when their canine ancestors came over from East Asia.
The problem is that you need big data sets for the kinds of comparisons he wants to make, and there aren't many nuclear DNA data sets for dogs just lying around.
Researchers are working on building them, he said. "[But] I think it will be a couple of years before you can try this specifically on American dogs."
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