Current breed standards defined by registries such as the AKC specify an 'apple-head' or 'apple-dome' skull conformation. Chihuahuas have large, round eyes and large, erect ears, set in a high, dramatically rounded skull. Chihuahuas can show traits from both Apple Head and Deer Head. 'Deer Head Chihuahuas tend to have better health than Apple Heads, due to their longer noses'. There is no scientific evidence that Apple Heads have a higher risk of getting respiratory issues, due to having a smaller airway. The result of crossbreeding Chihuahuas with other dog breeds such as Pomeranian dogs, Pembroke Welsh Corgis, Boston Terriers, Pugs and so on, usually ends up in a dog breed of a Chihuahua's body size and the other parent breed's coat color and fur traits.