• genome-wide association study;
  • horns;
  • quantitative trait locus mapping;
  • RXFP2;
  • Soay sheep

The chase to uncover the genetic underpinnings of quantitative traits of ecological and evolutionary importance has been on for a good while. However, the potential power of genome-wide association studies (GWAS) as an approach to identify genes of interest in wild animal populations has remained untapped. Setting technical and economic explanations aside, the sobering lack of success in human GWAS might have fed this restraint. Namely, while GWAS have successfully identified genetic variants associated with hundreds of complex traits (e.g. Ku et al. 2010), these variants have generally captured only a low percentage of variance in traits known to be highly heritable—an observation came to be known as the ‘missing heritability’ (Maher 2008; Aulchenko et al. 2009). Hence, if the vastly resourced human studies have been unsuccessful (but see: Yang et al. 2010), why should we expect that less resourced studies of wild animal populations would be able do better? In this issue of Molecular Ecology, Johnston et al. (2011) prove this line of thinking wrong. In an impressive and what may well be the most advanced gene mapping study ever performed in a wild population, they identify a single locus (RXFP2) responsible for explaining horn phenotype in feral domestic sheep from St Kilda (Fig. 1). This same locus is also shown to account for up to 76% of additive genetic variance in horn size in male sheep: this contrasts sharply with most human GWAS where mapped loci explain only a modest proportion of genetic variation in a given trait.


Figure 1.  The Soay sheep of the St Kilda archipelago are a primitive feral breed of domestic sheep. Pictured are a male with vestigial horns (=‘scurred’; left) and two normal-horned males (centre and right). Photograph courtesy of Peter Korsten.

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