I've been speaking a lot about dogs and dog breeds on this blog, but, did you know that estimated there are over 400 breeds of dogs in the world? It's true! It's because two different breeds of dog mate causing a new breed of dog when pregnancy occurs. When these puppies are bred, they are called mixed breeds. One example of a mixed breed is the chug. It is a combination of the pug and the chihuahua. Mixed breed dogs make up a huge percentage of the dogs in the world, so it really is impossible to put a single finger on it, due to the amount of new breeds being introduced all the time.