Maybe it is not just sentimental. Perhaps the connection to "man's best friends" is literally in our heads.
Skull shape is a complex trait, involving multiple genes and their interactions. Thanks to standardized canine breeding, which documents more than 400 breeds worldwide, and their distinct morphological features, researchers can disentangle traits such as skull shape, which is often a breed-defining variation.
For example, researchers are beginning to identify which genes cause a Bulldog or a Pug to have short pushed-in faces, or brachycephaly, and those that cause Saluki's or collies to have narrow, elongated snouts, or dolichocephaly. Between these two distinct canine cranium shapes are many variations that are also breed specific but can't be neatly categorized as brachycephalic or dolichocephalic, such as the rounded skull of the Chihuahua or the downward pointing snout of the Bull terrier.
Researchers now use genome-wide association studies (GWAS) to identify loci of interest that may be associated with these kinds of subtle differences. And that matters because craniofacial development is regulated similarly in canines and humans. Learning about dogs as model organisms can advance human health and biology, like helping children born with craniofacial deformities.
In humans these deformities include Apert, Crouzon and Pfeiffer syndromes, where skull bones fuse prematurely causing facial malformations, such as wide-set bulging eyes and broad foreheads, resulting in dental, eye and other physiological problems.
Writing in Genetics, Jeffrey J. Schoenebeck, PhD, and Elaine A. Ostrander, PhD, researchers at the National Human Genome Research Institute (NHGRI), review progress in defining the genes and pathways that determine canine skull shape and development that have been made in the eight years since the dog genome was mapped.
The use of GWAS in determining genetic variation in dogs is in its infancy. What's exciting, said Schoenebeck, is that with these studies and the tools researchers now have to map these variations "we may find new roles for genes, never before implicated in cranium development" and because similar genes and genetic pathways operate in humans, unexplained craniofacial developmental defects may become better understood.
Identifying the causative genetic mechanisms of these variations in canines offer researchers who study human cranial abnormalities "a way to figure out what sort of genetic variation matters and what doesn't," said Ostrander.
Citation: Jeffrey J. Schoenebeck and Elaine A. Ostrander, 'The Genetics of Canine Skull Shape Variation', Genetics February 2013 193:317-325; doi:10.1534/genetics.112.145284