Most dog lovers are aware of the hairless variety of the Chinese Crested dog, but did you know that there are also several other breeds of dog that are hairless as well? The state of being hairless is a trait that is considered to be a defining and desirable characteristic of the breeds in question, but it is actually caused by a genetic mutation. In breeds that are renowned for hairlessness, like the Chinese Crested, furry varieties of the dog are regularly produced as well.
As with everything else that makes up the hereditary traits of the dog, genetics are responsible for hairlessness. A genetic mutation causes hairlessness within bald canines, and hairlessness can be caused by either a dominant or recessive gene mutation.
A dominant gene mutation is one that is likely to override the normal genes, so that a dog carrying a dominant gene for hairlessness is much more likely to produce hairless offspring than one carrying a recessive hairless gene. The presence of dominant genes for hairlessness means that human intervention and selective breeding is not necessary to continue the lines of hairless dogs, and the breed will evolve naturally with hairless dogs being born in subsequent generations.
Where recessive genes are responsible for hairlessness, the likelihood of producing hairless offspring is lower, unless two dogs containing a copy of the recessive gene are mated, which raises their chances. This would generally be achieved by selective breeding.
However, some varieties of the recessive hairless gene are considered to contain a homozygous prenatal lethality, meaning that if two copies of the responsible gene are present (which is necessary with recessive genes to produce the trait in question) the puppies will spontaneously abort. There are various hairless dog breeds that are now extinct due to carrying the gene makeup for homozygous prenatal lethality, such as the African Hairless Dog and the Siamese Hairless Dog.
When two hairless dogs of the same breed and containing a dominant gene for hairlessness are mated, around a third of their resultant puppies will be born with hair, while the remaining two thirds will be hairless.
When a hairless and a furry dog of the same breed are mated, half of the resultant puppies will have fur, and half will be bald.
Where two furry dogs, even from within breeds known for hairlessness are mated, the chances are that all of their puppies will have fur.
There are four widely recognised pedigree dog breeds that are hairless, as well as a couple of other breeds that carry a dominant gene for hairlessness but that are not recognised by any main breed authority.
The Chinese Crested dog does not actually originate in China, but is most likely to hail from Africa. The Chinese Crested is equally well known for both hairless and furry dogs of the breed, with both varieties being widely recognised.
The hairless version of the Chinese Crested is not totally hairless, and will usually possess tufts of fur on its legs, tail, and on the top of the head.
The hairless Chinese Crested dog also has a rather unusual dental makeup, with most of their teeth being shaped like canine teeth as opposed to the usual combination of canines, molars and premolars most commonly seen in other dogs.
The Mexican Hairless dog or “Xoloitzcuintli” was historically thought to be related to the Chinese Crested dog due to its hairlessness and roughly similar body shape, but recent DNA testing has proven that this is not the case. They have been around in their native Mexico for over 3,000 years, and as they evolved naturally rather than as the result of human intervention and selective breeding, are considered to be a very robust and healthy dog despite their hairlessness gene mutation, and are not prone to any particular genetically inherited diseases. The Mexican Hairless dog may, however, have the unusual tooth structure commonly seen in the Chinese Crested dog, which is thought to be an additional manifestation of the gene responsible for hairlessness.
The Peruvian Hairless dog is sometimes known as the Peruvian Inca Orchid, and while furry versions of this dog are also produced, only the hairless variety is recognised under the breed standard. Like the Chinese Crested dog, they may have an unusually high number of canine teeth, and may display tufts of hair on the top of the head, on the legs and on the tail. Again, the Peruvian Hairless dog is not considered to be related to the Chinese Crested, other than by means of the usual remote genetic connection between all dogs of all types!
The Peruvian Hairless dog comes in three different sizes, being of course small, medium and large. The large version of the breed can stand up to 65cm tall, and weigh up to 25kg, but they are always on the slender side comparatively to their build.
The American Hairless terrier evolved from the fur-coated American Rat terrier, but is now recognised as a breed in its own right. They contain all of the personality traits of the average terrier, including a well-honed hunting instinct, but minus the fur coat!
With there being a relatively small amount of hairless dog breeds in the world, comparisons are often made between the four hairless breeds, and they are often thought to be related. However this has not been proven to be the case, and particularly in the case of the American Hairless terrier, genetic testing has demonstrated no common ancestry with any of the other extant hairless dog breeds.
Unlike the other three hairless dog breeds mentioned, the American Hairless terrier has normal tooth development, and does not demonstrate a lack of premolar teeth or an increased number of canine teeth.
At the time of writing, there are at least two other breeds of dog that are known to produce hairless varieties with a reasonable degree of regularity: the Hairless Khala, and the American Crested Sand Terrier.
However, neither of these hairless dog types are currently recognised by any major breed registry as legitimate hairless dog breeds in their own right.