Mutt's Day is observed on July 31, 2017. A mongrel, mutt, or mixed-breed dog is a dog that belongs to no single organizationally recognized breed and is not the result of selective breeding. Mutt is commonly used in the U.S.A and Canada, often in an affectionate manner.
When breeds mix, their offspring manifest a wide variety of appearances; some resembling one breed closely, while others clearly exhibit features of both. However, as mixed breeds continue to interbreed, subsequent generations moderate toward a roughly similar appearance. (With material from: Wikipedia)