How do you know your dog is full breed?

You can tell if a black lab is purebred by looking to see if you see any other dog breed in him/her. Example: if you see wrinkles, it might have been mixed with a Shar Pei or bulldog. If there is a black tongue, it could have been mixed with a chow chow. If you see any other colors on him/her then no, he/she is a cross breed. If it is ALL black and LOOKS exactly likes a lab, it will most likely be a pure bred lab!