A few of my recent posts have generated some questions/comments about similarities between individuals within a breed versus individual variation. This brought to mind a paper that appeared in the May 21, 2004 edition of the journal Science. It was titled "Genetic Structure of the Purebred Domestic Dog." It made quite a splash when it came out almost eight years ago now, and it’s still pertinent. I thought I would highlight a few passages from the paper here.

In brief, the researchers studied the genetic relationships between 85 diverse breeds of domestic dogs. They found that "differences among breeds accounted for ~30% of genetic variation," which can also be read that ~70% of genetic variation could not be accounted for by breed. Nonetheless, the scientists were able to come to some fascinating conclusions about how various breeds have developed.

The paper starts with the following:

The domestic dog is a genetic enterprise unique in human history. No other mammal has enjoyed such a close association with humans over so many centuries, nor been so substantially shaped as a result. A variety of dog morphologies have existed for millennia, and reproductive isolation between them was formalized with the advent of breed clubs and breed standards in the mid–19th century. Since that time, the promulgation of the "breed barrier" rule — no dog may become a registered member of a breed unless both its dam and sire are registered members — has ensured a relatively closed genetic pool among dogs of each breed. At present, there are more than 400 described breeds, 152 of which are recognized by the American Kennel Club (AKC) in the United States (1) … understanding the genetic relationships among breeds will also provide insight into the directed evolution of our closest animal companions.

The middle sections of the paper are dedicated to materials, methods, and results. Take a look at a ^†reprint if you are interested in the details (including some cool figures showing which breeds are most closely related to one another and to ancestral dogs) or want to see the references, but I’ll jump to the conclusions.

Our results paint the following picture of the relationships among domestic dog breeds. Different breeds are genetically distinct, and individuals can be readily assigned to breeds on the basis of their genotypes. This level of divergence is surprising given the short time since the origin of most breeds from mixed ancestral stocks and supports strong reproductive isolation within each breed as a result of the breed barrier rule…

Dog breeds have traditionally been grouped on the basis of their roles in human activities, physical phenotypes, and historical records. Here, we defined an independent classification based on patterns of genetic variation. This classification supports a subset of traditional groupings and also reveals previously unrecognized connections among breeds. An accurate understanding of the genetic relationships among breeds lays the foundation for studies aimed at uncovering the complex genetic basis of breed differences in morphology, behavior, and disease susceptibility.

Dr. Jennifer Coates

^† To read the study, Genetic Structure of the Purebred Domestic Dog, you can follow one of these links:

www.princeton.edu

www.britainhill.com

Or you can download the PDF here.

Image: cynoclub / via Shutterstock