All dogs, even cute little lap dogs, are ultimately descended from domesticated wolves.
There are hundreds of dog breeds with extremely varied characteristics and sizes, from the tiniest teacup Chihuahua to the hugest Mastiff, but all of these breeds make up just one species Canis lupus familiaris and can theoretically breed with one another (although there can be practical and health related constraints.) The dog was the earliest domesticated animal.
Dogs are red-green colorblind.
Dogs can hear much lower frequencies than humans, over twice as high as humans, and about four times as far as humans.
