by Dr. Kristopher J. Irizarry, PhD | May 01, 2013
The field of genetics has provided a number of insights into physiological basis of dogs and dog breeds and, in the process, we have realized that some of our ideas about dogs are not scientifically founded. What’s in a GENE? The problem with trying to guess what breeds of dog make up a mixed breed is that the traits associated with specific breeds are controlled by surprisingly few genes in the dog genome.
The canine genome was sequenced in publicly released in December of 2005, since that time many genetic studies have been conducted whereby saliva or blood from members of specific breeds is used to look for shared genes among members of the same breed. Some of these findings have elucidated genes associated with health problems while other studies have identified specific genes that are associated with specific breed defining visual traits such as coat color, coat length, body size and head shape, to name a few.
Interestingly, many people try to determine the breed composition of a mixed breed dog by looking at visual traits and mentally assigning those traits to different breeds. This practice has been accepted for quite some time, decades, maybe even hundreds of years. However, what genetics tells us is that visually assigning breed doesn’t work. The truth is people can’t do it. Some may think with training or practice one might be able to improve, but that’s not the case.
The problem with trying to guess what breeds of dog make up a mixed breed is that the traits associated with specific breeds are controlled by surprisingly few genes in the dog genome. In humans, we know that identical twins look the same because they share the same DNA. It is natural to assume that dogs with a similar visual physical appearance probably share the same DNA, but genetic studies have shown us why that assumption is incorrect.
In a 2010 paper entitled “a simple genetic architecture underlies morphological variation in dogs” by Boyko et al, geneticists analyzed more than 60,000 regions of the dog genome that are known to be variable between dogs and breeds. They specifically looked at 915 dogs from 80 dog breeds–corresponding to 55 million data points (60,000 times 915 = 54,900,000). Their findings are very surprising and show that the major breed defining traits in dogs, such as body size, ear shape, length of legs, coat color, length of fur, head shape and length of snout are controlled by very few regions of the genome. In fact, the authors of the study state that only roughly 50 regions control all of these traits. Some of the exact same versions of these genes are found in many different breeds which means that a mixed breed dog might have the size and shape of a certain breed without being even a little bit that breed!
So unlike humans, in which identical twins share all of their DNA, in dog breeds, like German Shepherds, there are surprisingly few genes controlling the physical appearance of the members of the breed. This unexpected result means that when you see a mixed breed dog about the size of a German Shepherd, with a long snout, erect ears and long black hair – it isn’t necessarily a German Shepherd, in fact, it may not even have any German Shepherd ancestors because those visual traits may be the result of about 10 genes in the dog’s genome. Considering that there are more than 20,000 genes encoded in the canine genome, what you see isn’t necessarily what you get when trying to guess what breeds make up a mixed breed dog. The take home message from this study is: “Don’t judge a dog by its external appearance.”