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Scientists Begin Untangling Genetics Behind Dog Breeds

NEW YORK (GenomeWeb News) – Scientists reported yesterday that they could unlock some of the genetic variation behind dog breeds by analyzing just a few thousand single nucleotide polymorphisms.
 
In a paper appearing in the latest issue of Genetics, a group of researchers from the US and the UK tackled the dog diversity represented by thousands of individuals from nearly 150 dog breeds. Based on characteristic breed traits, combined with SNP analysis of representatives from these breeds, the team found quantitative trait loci for features such as size, behavior, and longevity.
 
“It establishes that breed stereotypes are very real,” co-author Elaine Ostrander, head of the National Human Genome Research Institute’s comparative genetics section, told GenomeWeb Daily News. “We can use that information in our mapping studies.”
 
Although they’re just 15,000 years or so removed from their wolf ancestors, dogs have expanded into hundreds of distinct breeds that are characterized by diverse physical features — such as size, color, and skull shape. These breeds also have different disease susceptibilities, behavioral patterns, and longevity.
 
Generally speaking, these differences tend to reflect high genetic heterogeneity across breeds. But within breeds there is usually relatively low heterogeneity, meaning specific traits usually spring from the same underlying genetic root.
 
Ostrander and her colleagues took advantage both of the genetic similarities between dogs of the same breed and of the extensive records kept about dog breeds. Rather than taking measurements of height, weight, longevity, behavior, and so on for each individual, they tapped the wealth of information about dog breeds.
 
“The idea is that you really can take advantage of breed structure,” Ostrander said. “All dogs that have a given trait have it for the same genetic reason.”
 
Last spring, some members of the same research team published a paper in Science that identified a single allele in a gene on chromosome 15 called insulin-like growth factor 1 or IGF1 that governs small size in dogs.
 
For the latest work, the researchers focused on relatively few genetic markers — about 1,500 SNPs — in saliva and blood sample DNA taken from 2,801 dogs representing 148 domestic dog breeds.
 
They then looked for associations between these SNPs and physical characteristics (gleaned from the published sources including the American Kennel Club’s breed standards), breed longevity (taken from dog owner surveys and other sources), and behavioral patterns in specific breeds — from trainability to boldness.
 
The investigators uncovered 26 different quantitative trait loci on 14 chromosomes that were significantly associated with 10 traits. These included characteristics such as height and weight, coat length, ear bend, tail curve, snout size and shape, longevity, and boldness.
 
The authors noted that the data available from this study does not provide deep coverage of the genome and may also include some false-positive associations. Even so, they say, it provides an example of the power of across-breed mapping, revealing new regions of interest in the dog genome that opens the door for more comprehensive analyses.
 
“In the future, genotyping platforms should offer deeper coverage of the genome (~50,000 well-placed and informative SNPs), more robust and balanced breed representation, and more dogs per breed (30-50),” they wrote.
 
Calling this study a launch pad for large-scale experiments, Ostrander said that “much, much denser whole-genome association studies are going to be needed in the future.”
 
For instance, the CanMap project, an international collaboration involving researchers from Cornell University, the University of California at Los Angeles, the NHGRI, and elsewhere, will look at more than 120,000 SNPs in order to achieve fine-scale resolution of this genetic variation in dogs, Ostrander said. Those studies, in turn, are expected to provide insights into everything from dog traits to human health to people’s pet selection.
 
“With further refinement and additional data, this method could be used to tailor products that may benefit the health of pets,” lead author Paul Jones, researcher at the Waltham Centre for Pet Nutrition in the UK, said in a statement. “In addition, genetic information about behavioral traits, such as trainability and temperament, could also help veterinarians identify the most lifestyle-appropriate pet for an owner.”

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