Abstract
BackgroundThere are around 400 internationally recognized dog breeds in the world today, with a remarkable diversity in size, shape, color and behavior. Breeds are considered to be uniform groups with similar physical characteristics, shaped by selection rooted in human preferences. This has led to a large genetic difference between breeds and a large extent of linkage disequilibrium within breeds. These characteristics are important for association mapping of candidate genes for diseases and therefore make dogs ideal models for gene mapping of human disorders. However, genetic uniformity within breeds may not always be the case. We studied patterns of genetic diversity within 164 poodles and compared it to 133 dogs from eight other breeds.ResultsOur analyses revealed strong population structure within poodles, with differences among some poodle groups as pronounced as those among other well-recognized breeds. Pedigree analysis going three generations back in time confirmed that subgroups within poodles result from assortative mating imposed by breed standards as well as breeder preferences. Matings have not taken place at random or within traditionally identified size classes in poodles. Instead, a novel set of five poodle groups was identified, defined by combinations of size and color, which is not officially recognized by the kennel clubs. Patterns of genetic diversity in other breeds suggest that assortative mating leading to fragmentation may be a common feature within many dog breeds.ConclusionThe genetic structure observed in poodles is the result of local mating patterns, implying that breed fragmentation may be different in different countries. Such pronounced structuring within dog breeds can increase the power of association mapping studies, but also represents a serious problem if ignored.In dog breeding, individuals are selected on the basis of morphology, behaviour, working or show purposes, as well as geographic population structure. The same processes which have historically created dog breeds are still ongoing, and create further subdivision within current dog breeds.
Highlights
There are around 400 internationally recognized dog breeds in the world today, with a remarkable diversity in size, shape, color and behavior
Individuals are selected on the basis of morphology, behaviour, working or show purposes, as well as geographic population structure
Another advantage is that linkage disequilibrium (LD) in dog breeds extends over 20–100 times longer genomic regions than in humans, which means that a smaller number of markers are required for genome-wide scans in dogs
Summary
There are around 400 internationally recognized dog breeds in the world today, with a remarkable diversity in size, shape, color and behavior. The isolation and small effective population size of modern breeds has resulted in widespread inbreeding and the expression of a large number of genetic diseases Many of these are among the most frequently occurring diseases in humans, such as cancer, heart problems, deafness, blindness and joint diseases [6,8,9,12,13,14]. The fact that purebred dogs are separated into genetically differentiated breeds and that they live in the same environment as humans, makes them an ideal model to map genes for human disorders [5,8,13] Another advantage is that linkage disequilibrium (LD) in dog breeds extends over 20–100 times longer genomic regions than in humans, which means that a smaller number of markers are required for genome-wide scans in dogs. This, together with the low haplotype diversity within LD regions and high degree of haplotype sharing among breeds [9,10,14,16], facilitates the identification of chromosomal regions where candidate genes are located
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