Physical appearance (predominantly determined by genes that influence the development of canine size and body mass, coat length, type and color, skull shape, leg length, ear and tail types), is known to be controlled by a very small number of genes relative to the overall number of genes contained in the canine genome (~20,000 or so in total). These genes can have both recessive and dominant variants and the variants present determine the physical traits seen. The presence of breed signatures does not guarantee that the dog will look like all detected breeds.
The Wisdom Panel breed signatures are defined by markers that are consistent with the presence of a particular breed in the background of a tested dog. However, these markers were not chosen to specifically cover the genes responsible for specific trait determinations from those breeds, as many markers are instead found in the parts of the genome that do not result in an outwardly apparent trait. Therefore, a mixed-breed dog could be a mix of three or four breeds, but have few traits evident from one or more of these breeds.
There are a number of examples where traits in the parents or grandparents are not necessarily evident in the offspring. Consider eye color in humans, for example. Brown eye color is dominant over blue and green eye colors, and yet, a brown-eyed mother can have a green-eyed child if she does not pass on the dominant brown eye color variant. Another example of the surprising effects you may see when mixing breeds, is to look at some of the designer dogs. So called designer dogs are custom combinations of two different pure breeds. Puggles, for example, are crosses between Pugs and Beagles, and labradoodles are crosses between Poodles and Labrador Retrievers. Often these designer dogs will look quite different to the two founder breeds, because they are a mixture of two very different sets of genetic backgrounds.
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