Genomic Regions Associated with Dermal Hyperpigmentation, Polydactyly and Other Morphological Traits in the Silkie Chicken

The Silkie chicken has been a model of melanoctye precursor and neural crest cell migration and proliferation in the developing embryo due to its extensive hyperpigmentation of dermal and connective tissues. Although previous studies have focused on the distribution and structure of the Silkie's pigment or the general mechanisms by which this phenotype presents itself, the causal genetic variants have not been identified. Classical breeding experiments have determined this trait to be controlled by 2 interacting genes, the sex-linked inhibitor of dermal melanin (Id) and autosomal fibromelanosis (Fm) genes. Genome-wide single nucleotide polymorphism (SNP)-trait association analysis was used to detect genomic regions showing significant association with these pigmentation genes in 2 chicken mapping populations designed to segregate independently for Id and Fm. The SNP showing the highest association with Id was located at 72.3 Mb on chromosome Z and 10.3-13.1 Mb on chromosome 20 showed the highest association with Fm. Prior to this study, the linkage group to which Fm belonged was unknown. Although the primary focus of this study was to identify loci contributing to dermal pigmentation in the Silkie chicken, loci associated with various other morphological traits segregating in these populations were also detected. A single SNP in a highly conserved cis-regulatory region of Sonic Hedgehog was significantly associated with polydactyly (Po). Genomic regions in association with silkie feathering or hookless (h), feathered legs (Pti), vulture hock (V), rose comb (R), and duplex comb (D) were also identified.