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Trait Relationships and Genetics in Dogs
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Scientists wondered: if a truncated motor pattern is exaggerated in a breed, will it be amplified in the DNA? The answer appears to be yes. Findings indicate that genes associated with herding, pointing and boldness are found in areas linked to brain development (Jones et al. 2008), and two gene variants tied to herding are in the same location as genes linked to schizophrenia in humans. This is not to say that Border Collies are borderline schizophrenics. But it does stand to reason that candidate genes associated with extreme behaviors include some that may be expected to play a role in regulating those behaviors. Genes tied to pointing are in the same area as cranial nerve development, and boldness is linked to genes that encode proteins affecting specific neural connections and signal transduction (the mechanism that converts a mechanical/chemical stimulus to a cell into a specific cellular response). Whereas small dogs are genetically predisposed to excitability, boldness has no relationship to size.

Health Linkages
In canine physiology, form, function and behavior are mixed up in ways we don’t fully understand, and it’s becoming increasingly apparent that health is part of the formula, too. For example, just as certain cancers tend to occur at higher rates within specific breeds, certain orthopedic diseases are linked to a dog’s size. Researchers found that the incidence of two specific polygenic orthopedic diseases (those affected by multiple genes) — hip dysplasia and patellar luxation — are allied with the same gene variant that’s associated with size (Chase et al. 2009). Additionally, scientists discovered that pancreatitis, which occurs more commonly in small dogs such as Cocker Spaniels, is also related to the size-gene variant. Selecting for growth rates may not be the cause of disease. Rather, it’s possible that size extremes upset the balance of genes that control disease.

Breeders and scientists are working hard to discover what and where the problems are and how to solve them. How much influence does any one trait have on another? Do early-onset health issues like allergies predict the debilitating illnesses dogs experience later in life, such as Addison’s disease, arthritis or even cancer? In a survey of blind guide-dog handlers conducted by the Morris Animal Foundation in 2008, we discovered that working Golden Retrievers have a less than 30 percent cancer rate, compared to a 62 percent cancer rate in the general breed population. Remarkable! Guide dog schools drop 75 percent of Goldens from their programs before the age of two due to any number of health issues, including chronic allergies. It’s possible that allergies are predictors of cancer, but that hypothesis hasn’t yet been studied.

Breeders want to know if they can remove deleterious genes that predispose dogs to fatal diseases and still hold on to desirable traits that create the essence of a breed. Getting rid of genes responsible for disease may dramatically change the way pedigreed dogs look and behave. Consider, for instance, the possibility that eliminating spinal degenerative disease will introduce inconsistency in tail carriage and gait, or that identifying markers for elbow dysplasia and removing carriers from the breeding population will affect the width of the chest, resulting in an appearance contrary to that described by breed standards, or how a breed is expected to move and even behave. If so, will we be willing to re-examine the definition of a breed as dogs who share characteristic appearance, function and a common gene pool, a Victorian-era mandate meant to suspend change in pedigreed dogs? What scientific findings in this decade will determine the breeding of dogs in the near future? Finding genetic traits and identifying their relationships to one another will assuredly be at the top of the list.

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This article first appeared in The Bark,
Issue 62: Nov/Dec 2010

Jane Brackman, PhD, is an authority on the cultural history of canine domestication and the author of two books on pets in 19th-century America. See her new pup, Barkley, and watch him grow on her blog.

doctorbarkman.blogspot.com

Image Credit: Amanda Jones

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