You also can't ALWAYS tell what something is by looking at it. I always tell this story, so forgive me if you heard it already!
I work with a shelter. We had a an apparently purebred pitbull female who came in pregnant. she was never claimed. she gave birth to pups who turned out to look like yellow labs. at 2 mos, they were put up for adoption and listed as pitbull labrador mix. Now, I answered more customer questions of "how can you say they have pitbull in them, they look nothing like pitbulls!"
And I would explain patiently over and over that we KNOW what the mother was because they were born here. We were guessing at the lab part. Even when they came back at 4 months for their rabies shots, they still looked like yellow labs..no sign of pitbull anywhere. So you see, it all depends on which genes are stronger...