How Dogs Came to Be—Part 2

21 October 2012
Published in Life
Written by  Kim Schuske
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How Dogs Came to Be—Part 2 Kim Schuske

Dogs come in every conceivable shape and size. They can be six pounds or 200 pounds. They can be six inches tall or three feet tall. Researchers have begun to decipher the genetics behind this variation in dogs. And they've found that only a few genes can cause major differences.

In the 1800s, people were fascinated with dogs. Breeding dogs for extreme physical traits was a hobby for many. Breeds were created with short or long legs, pointy or floppy ears, smooth or coarse hair—in all possible combinations. In fact, 80% of the 300 plus dog breeds we have now, were created during this time. Robert Wayne, professor of ecology and evolution at UCLA, calls this period the third stage of dog evolution.

“We like to think of three stages, the first being this very early one where wolves interacted with hunter gatherers moving around the landscape. Then a second stage during the development of agriculture when human societies were more sedentary people began to live in small towns. Then we like to think of the third stage as the Victorian explosion of dog forms. What we see today is principally a product of that explosion over the last few hundred years.”

No other animal species in the world comes in such different sizes and shapes than dogs. How were breeders able to do this? Dog geneticists like Elaine Ostrander with the National Human Genome Research Institute are now solving this mystery. Ostrander says in twenty short years, dog researchers have now put together most of the tools needed to tell the story of the dog. She adds, genetic maps and sequencing the dog genome has allowed researchers to focus on many questions. “Whether it was behaviors, morphologic traits, why are dogs big, why are dogs small. Or diseases, why does this breed get cancer, why does this breed get epilepsy, why does this breed get diabetes.”

One of the first researchers to connect physical traits of dogs with genes was Gordon Lark, Professor Emeritus at the University of Utah. He started with the Portuguese water dog, which was bred to help Portuguese sailors on their fishing ships. One member of this breed, Bo, is now living with the Obama family in the White House. Lark started the project when his dog Georgie died.

“This dog, which I loved very much, when it died I realized the cure for this was to get another one fast. So I was looking for another Portuguese water dog and finally found a breeder who would let me have one. She said, ‘but I need to know what you do because sometimes people do things that are inappropriate for having this type of dog.’ So I said I was a soybean geneticist and what she seemed to hear was blah blah genetics blah blah.”

Lark says the breeder called him two or three times a week to talk only about genetics. “So when the time came for me to get the dog I said ‘well you know this has been a lot of fun talking and so on, but we haven’t talked money, I need to send you a check.’ And she said, ‘I’m giving you a very expensive dog free so that you will work on dog genetics.’ And that was actually the start of it.”

Lark and his colleagues contacted breeders and owners who gave DNA samples, X-rays, and all types of measurements of their dogs including body size, tail and ear length. “Well the first thing we found out blew us away. There is a trade off in shape, for instance in the legs being long and thin or being short and thick. And at the same time whether the pelvis was fairly robust or was like popeye the sailor man, a very narrow pelvis. And we were working with a colleague Dave Carrier here and he said ‘well that’s the difference between a greyhound and a pit bull. It’s the difference between energy efficient speed and power but slow.’”

Lark says the data helped explain how breeders could easily mix and match physical traits because they found only a few genes are controlling pelvis and leg shape at the same time. Lark, Ostrander and others have since discovered that a small number of genes have a big impact on many other traits. For example, one key gene is critical for whether a dog is big or small. By contrast, in humans it’s thought that height is controlled by at least 50 genes, says Ostrander. “We began to realize that there was a recurring theme in our work and that is for most of the traits that we study. It isn’t as though there are hundreds and hundreds of genes controlling that trait, but there really seem to be a small number of major effective factors.”

Surprisingly, just like what was found for physical traits, scientists are finding that a few genes are also responsible for diseases in dogs. Ostrander says because of inbreeding, purebred dogs are frequently prone to getting certain diseases. It turns out that many of these diseases are ones that humans also get. “Almost any disease I named off the top of my head that was common to humans occurred in dogs. Whether it be cataracts, epilepsy, or cancer, or diabetes.”

UCLA’s Robert Wayne says the simple genetics in dogs makes it easier to identify genes, including disease genes. By finding the genes first in dogs, it might narrow the search for disease genes in humans. “Because of the nature of how dogs were selected, very intensely by humans. It tends to be a simple genetic basis for many of the traits we observe. One or a few genes explain most of the variation we observe. So that makes the task of finding a gene much easier.”  

The gene for the sleeping disorder narcolepsy was found in dogs in 1999. This discovery led researchers to the cause of the disease in humans one year later. Recently a gene for Obsessive Compulsive Disorder was found in Doberman Pinchers. Researchers are now looking at that same gene in humans who suffer from OCD. And there many other promising studies, including for cancer that are currently under way.

Gordon Lark says the interesting thing about dog genetics research is that it’s a partnership with dog owners. “The dogs have never been kept in a laboratory, they are all owned by people. It’s just like human genetics. These owners really wanted to help.”

Once again dogs and people are working together, this time to advance our knowledge about how genes controlling physical traits and disease came to be.

This story originally aired 9/27/09

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