Body size

Body size in dogs is an adaptive trait that can be inherited and has been associated with variants present in several genes, such as IGF1 and IGF1R.

Definition

The body size of dogs is primarily determined by genetic factors, although also influenced by environmental aspects such as diet, care, age, and the dog's general health. Among the key genes in this determination, IGF1 (insulin-like growth factor 1) stands out as one of the main genetic determinants of canine body size, and appears to be fixed in almost all small dog breeds. In addition, IGF1R (IGF1 receptor) also contributes to size reduction, especially in dogs of diminutive sizes. Although other genes also influence size determination, IGF1 is considered a fundamental genetic factor in its estimation.

Genetic basis

The presence of two copies of either of the two analyzed variants in the IGF1 and IGF1R genes significantly increases the likelihood that the dog will exhibit a small body size. Conversely, the absence of these variants increases the likelihood that the dog will develop a large body size. In the event that there is only one copy of the variant, an intermediate phenotype may be present. It is important to note that body size in dogs can be influenced by other variants that have not been identified or analyzed in our test; therefore, the presence or absence of these two variants does not definitively ensure that the dog will be smaller or larger.

Other relevant information

The IGF1 (insulin-like growth factor 1) gene is a strong genetic determinant of body size in mammals and has been implicated not only in dogs but also in mice and even humans. Some large breed dogs have been found to have the variant described here. On this basis, we hypothesise the existence of an as yet unidentified locus associated with body size, which, through an epistatic relationship, may modulate the effect of this variant in some large dog breeds.

Bibliography

Hoopes B.C., Rimbault M., et al. The insulin-like growth factor 1 receptor (IGF1R) contributes to reduced size in dogs. Mamm Genome. 2012 Dec; 23(11-12): 780–790.

Rimbault M, Beale HC, Schoenebeck JJ, et al. Derived variants at six genes explain nearly half of size reduction in dog breeds. Genome Res. 2013 Dec;23(12):1985-95.

Sutter N.B., Bustamante C.D., et al. A Single IGF1 Allele Is a Major Determinant of Small Size in Dogs. Science. 2007 Apr 6; 316(5821): 112–115.