Abstract: The black shank trait favored by Chinese consumers is controlled by recessive sex-related gene or autosomal dominant gene. To explore the inheritance and molecular basis of black shank trait in a cultivated W strain, this study first conducted reciprocal crossing test between mature male and female chickens (1♂∶5♀) from the W line (black feather black shank) and the Rhode Island Red line (yellow feather yellow shank), followed by transcriptome analysis on the shank skin samples collected from the female offspring (4 chicks with black shank and 4 chicks with yellow shank) of the reciprocal crosses. The results showed that there were 293 chicks with black shank (♂172, ♀121) and 51 chicks with yellow shank (♂20, ♀31) in the cross of the W line with the Rhode Island Red line, there were 256 chicks with black shank (♂156, ♀100) and 73 chicks with yellow shank (♂29, ♀44) in the reciprocal cross, the offspring of both crosses had two shank colors, and the number of the chicks with black shank was significantly higher than that with yellow shank in each cross, indicating that the black shank trait of the W line belongs to autosomal dominant inheritance. Based on the statistics of shank color and feather color in the offspring of the breeding groups with shank color separation, it was found that the chicks with black shank had black feathers and the chicks with yellow shank had yellow feathers, the number of the chicks with black shank to that with yellow shank (121∶117) conformed to the separation ratio of 1∶1, suggesting that the black vs. yellow shank traits in the cultivated strain were controlled by a pair of alleles. The transcriptome analysis of shank skin samples showed that the differentially expressed genes (DEGs) were significantly enriched in Melanogenesis pathway (P < 0.01), the expression of Mc1r and the genes, such as Tyr and Tyrp1, which are known to be involved in the regulation of melanin synthesis was significantly different between black and yellow shank skin samples, and some other genes, such as Wnt16, Wnt3a, Fzd10, that are not previously reported to be involved in shank color formation, also showed significant difference. In addition to the Melanogenesis pathway, black shank formation was also involved in extracellular matrix and receptor signaling, signal transduction, cell cytoskeleton and migration, cell adhesion, sphingolipid and glycolipid metabolisms. In conclusion, based on genetic analysis and transcriptome analysis, this study inferred that the black shank trait in the cultivated W strain was regulated by Mc1r gene, was inherited in autosomal dominant mode, the formation of black shank trait involved multiple signaling pathways, which laid a foundation for clarifying the mechanism underlying formation of black shank trait.

Key words: chicken, shank color, dominant inheritance, autosomal inheritance, Mc1r