What dog breeds were used to create the Chihuahua?

There are two theories regarding the origin of the Chihuahua. One theory is that they are descended from a small dog called the Techichi, which was kept by the Toltec civilization in Mexico. The other theory is that they were brought to Mexico from China by Spanish explorers.

However, according to the American Kennel Club, the Chihuahua is a native of Mexico and is not related to any other dog breed.