Finally, Fido has a proper family tree.

Genetic researchers have assembled the most definitive evolutionary tree of dogs using gene sequences from 161 modern breeds. The map of dog breeds and how they are related, the largest to date, may eventually help researchers identify disease-causing genes in dogs and humans.

The study was published April 25 in Cell Reports.

Researchers found new evidence that dogs traveled with Native American ancestors who crossed the Bering Strait. Scientists have previously reported that such a New World Dog existed, but this study marks the first time genetic evidence of this ancient canine sub-species has been identified in modern breeds.

Some dogs from Central and South America, including the Peruvian Hairless and the Xoloitzcuintle, are likely descended from the New World Dog. These breeds are genetically distinct from popular breeds in American, most of which are of European descent.

"What we noticed is that there are groups of American dogs that separated somewhat from the European breeds," said study co-author and dog geneticist Heidi Parker of the Nation Institutes of Health. “We’ve been looking for some kind of signature of the New World Dog, and these dogs have New World Dogs hidden in their genome.”

It’s unclear precisely which genes in modern hairless dogs are from Europe and which are from their New World ancestors, but the researchers hope to explore that in future studies.

The large genome dataset the geneticists assembled, including pure breeds sampled from around the globe, helped them account for mechanisms that led to the formation of modern breeds. The researchers propose that breed creation was a two-step process: dogs were bred first to fill certain functional roles, then for certain physical attributes.

“First, there was selection for a type, like herders or pointers, and then there was admixture to get certain physical traits,” said Parker. “I think that understanding that types go back a lot longer than breeds or just physical appearances do is something to really think about.”

The researchers amassed a dataset of 1,346 dogs originating from all continents except Antarctica. To collect the material for gene sequencing, they attended dog shows and recruited dog owners to participate in the study.

“If we see a breed that we haven’t had a good sample of to sequence, we definitely make a beeline for that owner,” said Elaine Ostrander, senior co-author and dog geneticist, also of the NIH. “And say, ‘Gosh, we don’t have the sequence of the Otterhound yet, and your dog is a beautiful Otterhound. Wouldn’t you like it to represent your breed in the dog genome sequence database?’ And of course, people are always very flattered to say, ‘Yes. I want my dog to represent Otterhound-ness.’”

The quest continues. More than half the dog breeds in the world today still have not been sequenced and the researchers intend to keep collecting dog genomes to fill in the gaps.

Dogs and people are subject to many of the same diseases, including epilepsy, diabetes, kidney disease and cancer, so understanding dogs’ genetic history may have practical applications in research, said Ostrander.

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