Derived variants at six genes explain nearly half of size reduction in dog breeds.
Level 5 - mechanism / opinion, no new human data
Animal genetic association and fine-mapping study
PubMed 24026177 · doi:10.1101/gr.157339.113
What was done
Fine-mapping was performed on four previously identified genome-wide association study loci (covering candidate genes GHR, HMGA2, SMAD2, and STC2) to pinpoint five highly associated markers. These markers, along with previously reported size-associated variants in IGF1 and IGF1R, were genotyped across 500 domestic dogs representing 93 breeds. Ancestral versus derived alleles were identified by genotyping 30 wild canids across the same markers. Investigators then evaluated the association between derived alleles and body size variance across dog breeds.
What was found
Derived alleles at all seven markers correlated with reduced body size, with smaller dogs harboring derived alleles at multiple loci. Across all evaluated dog breeds, the seven markers explained 46.0% to 52.5% of the variance in body size. In breeds with standard weights under 41 kg (90 lb), these genotypes accounted for 64.3% of the variance in body weight. Most breeds were not fixed at all markers, displaying multiple genotype combinations within breeds.
Why it matters
The findings show that a small set of derived genetic variants across six growth-regulatory genes drove a substantial portion of artificial selection for reduced body size in domestic dogs. This provides a clear model for how major-effect alleles shape morphological diversification in mammals.
Limits
The study is restricted to canines and does not evaluate human populations. The analyzed markers explain less variance in giant breeds (>41 kg), indicating uncaptured genetic determinants in large dogs. The abstract does not report individual-level weight measurements versus breed standards, and the functional causality of specific variants was hypothesized rather than experimentally proven.