Abstract
Shank skin color of Korean native chicken (KNC) shows large color variations. It varies from white, yellow, green, bluish or grey to black, whilst in the majority of European breeds the shanks are typically yellow-colored. Three shank skin color-related traits (i.e., lightness [L*], redness [a*], and yellowness [b*]) were measured by a spectrophotometer in 585 progeny from 68 nuclear families in the KNC resource population. We performed genome scan linkage analysis to identify loci that affect quantitatively measured shank skin color traits in KNC. All these birds were genotyped with 167 DNA markers located throughout the 26 autosomes. The SOLAR program was used to conduct multipoint variance-component quantitative trait locus (QTL) analyses. We detected a major QTL that affects b* value (logarithm of odds [LOD] = 47.5, p = 1.60×10−49) on GGA24 (GGA for Gallus gallus). At the same location, we also detected a QTL that influences a* value (LOD = 14.2, p = 6.14×10−16). Additionally, beta-carotene dioxygenase 2 (BCDO2), the obvious positional candidate gene under the linkage peaks on GGA24, was investigated by the two association tests: i.e., measured genotype association (MGA) and quantitative transmission disequilibrium test (QTDT). Significant associations were detected between BCDO2 g.9367 A>C and a* (PMGA = 1.69×10−28; PQTDT = 2.40×10−25). The strongest associations were between BCDO2 g.9367 A>C and b* (PMGA = 3.56×10−66; PQTDT = 1.68×10−65). However, linkage analyses conditional on the single nucleotide polymorphism indicated that other functional variants should exist. Taken together, we demonstrate for the first time the linkage and association between the BCDO2 locus on GGA24 and quantitatively measured shank skin color traits in KNC.
Highlights
Genetic studies of shank skin colors have long history
The carotenoid pigmentation is affected by carotenoid in feed, while the melanin pigmentation is affected by the melanocytes in the dermal and epidermal tissue
In common with Knox, the autosomal dominant W locus is known to be responsible for the dominant white (W+) and recessive yellow (w) shank skin colors, which are related to the carotenoid pigmentation
Summary
Genetic studies of shank skin colors have long history. In 1935, Knox investigated the qualitative inheritance of shank skin colors in chickens (Knox, 1935). The extended black (E) locus affects epidermal melanization, which is associated with dark shank skin colors. Causal genes responsible for Mendelian shank skin color variations were identified in chickens. Five lines of KNC have been established and they are classified mainly based on plumage colors [Gray-Brown (G), Black (L), Red-Brown (R), White (W) and Yellow-Brown (Y); DAD-IS; http://dad.fao.org/]. When these lines were established, the selection criteria for shank skin color was charcoal gray or dark green colors so as to differentiate from commercial broilers which have yellow shanks.
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