Now that can be solved with a simple test.
"Very easy, it's just a quick swab in the mouth, it takes less than five seconds, and you send it away and get the results in less than three weeks," said Michael Morefield.
Morefield manages the Arizona Animal Welfare League.
It's the first shelter in the state that has DNA testing for dogs.
He says the tests allow people to know which dog will best fit for their family.
"So we can have these great conversations with people about what animal they're adopting since it is such a long-term commitment," said Morefield.
Paul has had the testing done; now he just needs a forever home.
By looking at Paul you may just think he's a rottweiler, but a DNA test show he's more than that, he needs an active family.
"Paul is a pure bred Rottweiler on one side, and a border collie on the other side," he said.
The tests go back to the dogs great grand parents. Morefield said the DNA tests will help prevent dogs from being classified into the wrong breed.
"When people go to shelters they think oh, it's all pit bulls and Chihuahuas and it's really not. It's this extremely diverse group of animals, and this DNA project is allowing us to see that," said Morefield.
Two-thirds of all dogs at the Shelter right now are getting their DNA tested.