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The Genetics of the Chinese Crested Dog

Updated on March 31, 2019
Teeuwynn Woodruff profile image

Teeuwynn has owned dogs her whole life. She has enjoyed the companionship of everything from Pugs to Newfoundlands.

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Hairless vs. Powderpuff

The Chinese Crested dog has two varieties. The hairless has a plume of hair on his tale, a crest of hair on his head and high “socks” along his lower legs and feet. The powderpuff has a full double coat of fur all over his body.

The other main difference between the two varieties is that the Hairless has a “primitive” dentition which can lead to loose, missing or lopsided teeth.

A team of European scientists led by Tosso Leeb, were interested in studying the root causes of hairlessness in some breeds of dogs. They studied the genetic material of over 20,000 dogs in their research.

Interestingly, due to dogs living so close to humans and being bred by humans dogs has a unique genetic history. In this domestication process we accidentally created genetic bottlenecks. These bottlenecks formed haplotypes (sets of DNA that are inherited together).

Since most dog breeds are developed over a hundred years or so, large chunks of genetic material stays the same from breed to breed and that helps researchers figure out all sorts of things about our dogs.

The Gene for Hairlessness

When researchers focused on the Chinese Crested they found that the hairless Crested, Peruvian Hairless, and Mexican hairless dogs all had the same 102,000 string mutation. None of the coated breeds had the mutation.

The researchers named one of the genes FOXAI3 because that gene has come up in other studies involving hair loss.

Researchers don't yet know how FOXI3 leads to hairlessness but they hope to soon figure it out.

The difference between Chinese Crested Powderpuffs and Hairless Chinese Crested on the FOXI3 genes.
The difference between Chinese Crested Powderpuffs and Hairless Chinese Crested on the FOXI3 genes. | Source
These powderpuffs both have the recessive (hrhr) gene combination.
These powderpuffs both have the recessive (hrhr) gene combination. | Source

But What If I Want To Breed My Chinese Crested

Knowing the genetic background information on your dog is a crucial step in being able to breed a healhy, happy, companion or show prospect. There are many other factors involved in deciding whether to breed, but this article is only going to focus on helping you decided to breed from a hairless/powderpuff side.

We'll take the breeding combinations one at a time. For the terms of this experiment we will assume we get an exact even distribution of puppies in each litter. In real litters this will often not be the case.

Remember, the gene for hairlessness is dominant, but if a fetus gets two of these dominant genes it does not form properly and will not make a puppy.

We will now go through the combinations of Hairless and Powderpuff to see what puppies will ON AVERAGE come from such a pairing.

Hr -- Gene for Hairlessness

hr - Gene for coatedness

Photo by Katarzyna Zienkiewicz
Photo by Katarzyna Zienkiewicz

Hairless to Hairless Breeding

Dam: Hairless (Hrhr)
Sire: Hairless (Hrhr)
 
puppy 1 (HRHR)
puppy 3 (Hrhr)
 
puppy 2 (Hrhr)
puppy 4 (hrhr)
 
 
 
 
In this breeding of two hairless parent's puppy 1 receives two copies of the Hairless gene, This puppy will die in utero. Puppy 2 and 3 will be Hairless and puppy 4 will be a powderpuff.
Photo by Katarzyna Zienkiewicz
Photo by Katarzyna Zienkiewicz

Hairless to Powderpuff Breeding

 
 
 
Dam: Hairless (Hrhr)
Sire: Powderpuff (hrhr)
 
puppy 1 (Hrhr
puppy (Hrhr)
 
puppy 2 (hrhr)
puppy (hrhr)
 
In this breeding, puppies 1 and 3 get the gene for hairlessness and become hairless themselves while puppies 2 and 4 do not and are powderpuffs.
This hairless Crested has the (Hrhr) genetic code.
This hairless Crested has the (Hrhr) genetic code. | Source
Photo by Katarzyna Zienkiewicz
Photo by Katarzyna Zienkiewicz

Powderpuff to Powderpuff Breeding

Dam: Powderpuff (hrhr)
Sire: Powderpuff (hrhr)
 
puppy 1 (hrhr)
puppy 3 (hrhr)
 
puppy 2 (hrhr)
puppy 4 (hrhr)
 
 
 
 
Since the powderpuff coat is caused by 2 recessive genes, all the puppies receive the recessive genes, so they are also powderpuffs.

Breeding Factors

Looking at the charts above shows that when two Hairless Chinese Cresteds are bred together 25% of the time their offspring with die in utero due to the fatal (HrHr) combination.

If two Powderpuff Chinese Crested are bred together you will only ever see Powderpuff puppies from the litter, so that deadly genetic combination will not arise.

In order to keep both varieties of the Chinese Crested going strong its important that many breedings be performed between one Hairless Crested and one Powderpuff Crested.

This hairless Crested has the (Hrhr) genetic code.
This hairless Crested has the (Hrhr) genetic code. | Source

Other Inherited Conditions

Chinese Crested dogs can suffer from several other inherited conditions -- some of which we can test our dogs for before breeding them.

The first four conditions affect the eye. They are: Progressive Retinal Atrophy (Generalized PRA & PRCD) and Primary Lens Luxation (Anterior Lens Luxation & Posterior Lens Luxation)

Progressive Retinal Atrophy is a group of conditions applying to the eye. There is bilateral degeneration of the retina and this causes progressive loss of sight and eventual blindness in the dog. PRA is inherited. Since it's a recessive trait, both parents must have the disorder or be carriers for their puppies to inherit it. There is no cure for PRA. Genetic testing isn't available for this form of PRA.

Progressive rod-cone degeneration (PRCD) is another type of Progressive Retinal Atrophy. In this form of the disease the rod cells in the eyes begin to degenerate with the cone cells following. Eventually, the condition leads to blindness. PRCD is an inherited, recessive condition. Genetic tests are available to determine whether a dog has this condition, is a carrier, or is free of the condition. There is no cure for affected dogs.

Primary Lens Luxation. Chinese Cresteds are prone to two forms of primary lens luxation. Both forms are inherited, recessive genes. Dogs can be tested to see if they are affected, carriers, or free of the condition. With primary lens luxation the suspensory fibers in the eye degenerate causing the eye lens to dislocate. There are two forms of PLL: Anterior Lens Luxation and Posterior Lens Luxation.

Anterior Lens Luxation. In this form of the disorder the lens luxate and push forward into the iris. Sometimes they actually enter the anterior portion of the eye itself. This can cause glaucoma or injury to the cornea. Surgery is required.

Posterior lens luxation. In this condition the lens falls back into the eye's vitreous humor. The lens can fall to the floor of the eye itself. Although less problematic than anterior lens luxation, this condition is usually treated with surgery.

Luxating Patellas. This is an inherited condition where the knee joint luxates, or pops, out of place. It can move to either the medial or lateral position. The luxation can be mild, moderate, or severe. In more severe cases it requres surgery to fix.

Before using a dog in a breeding program have your dog genetically tested for PRCD and Primary Lens Luxation. You should also have your dog examined by a qualified member of the Orthopedic Foundation for Animals.

A very young Chinese Crested puppy out in the air.
A very young Chinese Crested puppy out in the air. | Source

A Brief Lecture on Mendelian Genetics

© 2014 Teeuwynn Woodruff

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