Where Did the Hairless Trait Come From?

Hairless dogs have been noted in many regions of the world for more than 500 years. The Xolo is the oldest hairless breed and one of the few breeds indigenous to the New World. The Xolo evolved naturally, in response to its environment.

Spontaneous genetic changes, known as mutations, are the basis of evolution and natural selection. Most of time, these changes are nonviable. Others are viable, but incapable of reproducing. Very rarely a spontaneous mutation occurs that is viable, fertile, and advantageous. The Xolo was one of these.

Hairlessness is one of the more common random mutations of mammalian species. Although the hairless trait first occurred as a spontaneous mutation, it has been documented in every breed of dog and has been intentionally perpetuated in many species such as hairless cats, rats, mice and guinea pigs.

The Dominant Hairless Trait

Hairlessness can be easily perpetuated because it is controlled by a dominant gene. In other words, mating a hairless dog to a normal dog will always produce some hairless puppies.

Because the trait is dominant, every dog that exhibits the trait is also capable of reproducing it. Hairless dogs have the genetic potential to produce both hairless and coated puppies.  This is because every hairless carries the (H) dominant hairless gene, as well as the (h) recessive hairless gene.  Every hairless dog can hand down to its progeny either hairlessness, or a full coat of hair.  The recessive expression of this gene will be masked unless it is paired with another recessive gene. That combination (hh) produces normal puppies. In the Chinese Crested these are known as Powderpuffs.

Statistically, one of every four puppies should be coated. Most breeders will confirm that the most litters do not match these predicted ratios. It is not unusual for litters to contain only hairless or powderpuff puppies. This remains true regardless of whether a hairless is bred to another hairless or to a powderpuff. The only predictable aspect of hairless genetics is that breeding two powderpuffs together will result in only powderpuff puppies.  This is because powderpuffs carry only the recessive genes for this trait. They cannot produce hairless puppies unless they are mated to a hairless.

Dentition of Hairless Dogs

Hairless Cresteds are not prone to any unusual health problems as a result of this trait. But it is associated with another unique feature. Dominant hairlessness is genetically linked to the trait for missing teeth. This combination of traits has been noted for more than 500 years. It is considered normal for hairless dogs and will not interfere with the dog’s ability to eat.  Because they do not carry the hairless gene, powderpuffs always possess normal dentition.

Many hairless Cresteds possess complete dentition. Others exhibit characteristic features of hairless dentition such as missing premolars and primitive tusk like canine teeth.

Puppies of both varieties possess a complete set of deciduous teeth. For the hairless variety, this does not guarantee that a complete set of adult teeth will follow. Puppy teeth can remain firmly in place for years if not disturbed by erupting permanent teeth.

Occasionally, retained deciduous teeth begin to compete for space with emerging adult teeth. This provides a perfect environment for tarter build up and periodontal disease. A far more serious consequence is permanent malocclusion due to overcrowding. This condition can progress into more than a cosmetic problem and can permanently affect your puppy’s quality of life.

Overshot, undershot, or wry bites are not genetically linked to hairlessness, although incomplete dentition can make it more difficult to evaluate these faults. Malocclusion can be dental or skeletal in origin, and these faults occur in every type of dog.

The Recessive Hairless Gene

The American Hairless Terrier

Like the Xolo and the Sphynx Cat, the American Hairless Terrier was created from  a spontaneous hairless mutation.  This hairless puppy was born into a normal litter or Rat terriers, in 1972. The AHT breed is unique in the fact that this manifestation of the hairless trait is transmitted as an autosomal recessive trait. This form of the hairless mutation differs in respects to both genotype and phenotype. Hairless AHT puppies are coated at birth, covered with a fuzzy coat that they gradually lose by weaning time. Even more interesting is the fact that recessive hairlessness is not genetically linked to the trait for missing teeth. It is fascinating to consider that this mutation has been genetically engineered in various fashions. Obviously, Mother Nature must be trying to tell us that it is a good idea.