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A hairless dog is a dog with a genetic disposition for hairlessnes. There are two known types of genetic hairlessness, a dominant and a recessive type.
Dogs with dominant genes for hairlessness can pass their attributes to their offspring in natural conditions, that is, not under the control of humans. Therefore, it is possible that, in some parts of the world, groups of hairless dogs came into existence. Later in history, people developed these groups into a recognized breed.
Known breeds at this time are the Chinese Crested Dog, the Mexican Hairless Dog, and the Peruvian Hairless Dog. Other breeds there are said to exist are the African Hairless Dog and the Thai Hairless Boran Dog.
This type of genetic structure is said to be homozygous lethal for the dominant gene. This means that dogs with two dominant genes cannot live. Therefore, all dominant-hairless dogs have a heterozygous gene structure. There's also a homozygous recessive type, which is a coated variety. On average, every litter of hairless puppies should come with some coated ones, too. Statistically, for every 2 hairless puppies, there should on average be one coated.
However, some breeders claim varying averages from 1:0 to 2:1; that is, some breeders claim to have no coated offspring in any of their litters, while others claim to have an average ratio of 8:1 or 4:1 or 2:1. Averages that show more coated than hairless are not known.
The Chinese Crested coated variety is called "Powder Puff", and is a recognized type. For the other breeds coated varieties are not recognized as valid varieties for show dogs.
Dogs with a recessive gene for hairlessness are not known in natural conditions. The only known such breed, the American Hairless Terrier, is created by mankind.
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