New genetic research may explain why Fluffy is so fluffy.

A study led by researchers at the National Human Genome Research Institute scanned 1,000 dogs from 80 breeds, looking for genes associated with different hair types: curly, wavy, straight, wiry, long and any combination of these. Their results, published online last week in Science, show that variations in just three genes account for nearly all of the different types of coats worn by man’s best friend.

The study found that purebred dogs with similar hair types were found to have similar variations at three particular genes, RSPO2, FGF5 and KRT71.

A particular variation in the RSPO2 gene was linked to wiry hair in a pattern that gives dogs a moustache and eyebrows, such as in a schnauzer.

A variation in the FGF5 gene was associated with long hair, whether silky or fluffy, like that in a Pomeranian. Variations in the KRT71 gene seem to affect the extent of hair curl in dogs like Irish water spaniels.

The FGF5 and KRT71 genes have been shown in previous studies to also affect hair type in cats and mice, suggesting that their effects may be relevant to all mammals, including humans.

Some dogs have all three of the variations identified by the researchers, including Portuguese water dogs, a breed you may have seen taking walks on the White House lawn.

Short-haired dogs like beagles, who don’t exhibit any of the different types of hair studied by the researchers, all seem to have the ancestral versions of the FGF5, RSPO2 and KRT71 genes. The study also found that wolves carry the non-mutated forms of these genes, suggesting that the different types of hair evolved after the evolutionary split between the two canine subspecies.

Despite what we know about the genetics of hair type in dogs, there is little known about what makes human hair straight, wavy, curly, frizzy, kinky, woolly or helical. While hair type in dogs is easily classified, studying human hair is not as simple. Some scientists have suggested characterizing hair by curl ratios and other measurements, but our diverse biological background poses a challenge in classifying human hair types for research.

This study could help researchers better understand the genetics of hair type in humans. It has also unleashed new possibilities for human disease research because these three genes that affect dogs’ coats also regulate many other processes in living organisms, giving researchers a chance to study how powerful genes interact with each other.

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On occasion, the Spittoon departs from its usual mission of bringing you the latest and greatest in human genetics news in order to report on particularly interesting discoveries in other species.  Many times these stories are about dogs and the reason is simple: dogs are awesome.

Well, there is more to it.  In addition to being faithful companions, dogs make great subjects for genetics research—the time between generations is much shorter in dogs than humans, they have multiple offspring per pregnancy and unlike in humans, it’s not unethical for scientists to decide which males and females breed together.

A luminary in the field of dog genetics is Elaine Ostrander, chief of the Cancer Genetics Branch of the National Human Genome Research Institute.  Her lab uses dogs to study cancer susceptibility genes, but along the way they’ve made some fascinating discoveries about the incredible variation seen between the many breeds that make up the single species Canis lupus familiaris.

In 2007 Ostrander’s group showed that small size in dogs—think Chihuahuas and Pomeranians—can be traced to a single variant of the canine IGF-1 gene.  Now, in a paper published online this week in Science Express, they have shown that a single evolutionary event is behind the short, curved legs characteristic of all those adorable dachshunds, corgis and basset hounds.

Ostrander’s group found that dogs having stubby little legs, technically termed chondrodysplasia, harbor an extra copy of a growth factor gene called FGF4.  But this is no ordinary gene duplication that happened as the result of a DNA replication error.  Instead, the researchers found that the extra copy of FGF4 is a retrogene, a piece of DNA copied from and then inserted back into the dog genome by a virus.

Retrogenes are nothing new.  They’re known to be a major source of genetic change that takes place as different species split apart from each other.  But this new study is the first to show that a retrogene can cause long-lasting variation within a species.

The various stumpy-legged dog breeds were developed in different places around the world, at different times and for various reasons.  So there’s no evidence that they share a recent common ancestor.  But the FGF4 retrogene appears to be identical in all of them, suggesting to the researchers that it arose only once, probably before early dogs split into modern breeds.

These new findings don’t just represent an advance in the understanding of dog genetics, or even the fundamentals of DNA and evolution.  They also have implications for human health.  The type of growth disorder seen in the dogs with the retrogene is reminiscent of hypochondroplasia, a type of dwarfism.  Scientists know that a mutation in one gene is responsible for most cases of this condition, but the cause of the rest remains a mystery.  According to Ostrander, her group’s results suggest that researchers interested in hypochondroplasia and other disorders of human growth and development should set their sights on FGF4.


More Spittoon posts about dogs and genetics:

• Gene Links Gout in Humans with Bladder Stones in Dalmatian Dogs
• Learning from Dog Eye Disorders

Picture Sources:

• Basset hound
• Dachshund

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