So many doggone traits: mapping genetics of multiple phenotypes in the domestic dog

Abstract

The worldwide dog population is fragmented into >350 domestic breeds. Breeds share a common ancestor, the gray wolf. The intense artificial selection imposed by humans to develop breeds with particular behaviors and phenotypic traits has occurred primarily in the last 200-300 years. As a result, the number of genes controlling the major differences in body size, leg length, head shape, etc. that define each dog is small, and genetically tractable. This is in comparison to many human complex traits where small amounts of variance are controlled by literally hundreds of genes. We have been interested in disentangling the genetic mechanisms controlling breed-defining morphological traits in the domestic dog. The structure of the dog population, comprised large numbers of pure breeding populations, makes this task surprisingly doable. In this review, we summarize recent work on the genetics of body size, leg length and skull shape, while setting the stage for tackling other traits. It is our expectation that these results will contribute to a better understanding of mammalian developmental processes overall.

Figure 1.

Genetic clustering of domestic dogs and gray wolves. The inner circle is a neighbor-joining tree representing the clustering of domestic dog breeds into ∼10 groups based on the comparison of 10-SNP haplotypes (tree originally published in (16)). The outer circle shows the five groups previously found from a microsatellite analysis of 130 breeds (22). Reproduced with permission from Mammalian Genome (45).

Figure 2.

Correlation of the allele frequency and size at IGF1 and IGF1R loci. The average height and weight of breeds from the CanMap dataset are plotted (3). Each circle represents one breed. The ancestral allele frequency is represented as a gradient from red (low) to yellow (high). SNPs depicted include CFA15:44,226,659 (A) and CFA3:43,756,620 (B). These SNPs are highly associated with canine body size at IGF1 and IGF1R loci, respectively (3,31).

Figure 3.

Skull shape variation in the dog. Above are shown extreme examples of brachycephalic breeds (on top, from left to right: Pug, Japanese Chin, Brussels Griffon, French Bulldog, Neapolitan Mastiff) and dolichocephalic breeds (on bottom, from left to right: German Shepherd Dog, Bull Terrier, Saluki, Ibizan Hound, Collie) (images: Mary Bloom, AKC).