Scientists have completed the first comprehensive comparison of the genes of domesticated dog breeds.

The analysis of 85 common types—including the Pekingese, Great Dane, Border collie, and dachshund—found fascinating clues about how dog breeds are related to one another, and how they may have descended from ancestral dogs in different parts of the globe. Those clues, in turn, could increase understanding about early human migration.

The findings, reported in tomorrow's edition of the research journal, Science, may also offer the first way to determine the breed of a dog based on a genetic sample. The majority of breeds tested have a unique DNA signature, despite the fact that many breeds were created only within the last few centuries.

"Since the formation