Study On The Melanogenic TYR5' Regulational Region And Agrp Gene Of Chicken Through SSCP

Melanin traits are the very important traits in chicken breeding. In this study, we selected tyrosinase (TYR)gene and agouti-relation protein(Agrp) gene as the candidate genes affecting melanogenic traits in chicken.We detected the polymorphisms of this gene by PCR-SSCP (single-strand conformation polymorphism) in F2 generation of resource families of chicken, and analyzed the genetic correlation between the polymorphisms of two genes and melanogenic traits by SAS8.10 in chicken.The tyrosinase plays a key role of melanogenesis in mammalian animal and bird. So we detected the DNA variation of 5'-regulatory partial region of chicken TYR by PCR-SSCP, then sequenced this region. We found there are four mutation homozygotes. The genetic correlations were obtained between genotypes of the 5' -region of TYR gene and melanogenic traits by the chi-square analysis. The results indicate that TYR could be a genetic locus or linked to a major gene which significantly affecting melanogenesis of skin color, shank color .meat color and bone membrane color in chicken .Agouti-relation protein is another candidate gene in this study. The Agrp gene was amplified by using six pairs of primers. Four polymorphisms were found in the chicken Agrp gene, they were detected by PCR-SSCP, and then confirmed by DNA sequencing. Two mutations were found in 5' -region and other mutations were found in exon region of Agrp gene respectively. The primer 1 of Agrp polymorphism involved G-A at nt -241 in the 5' flanking region upstream from the transcription initiation site of the gene, and a significant associations between the primer pair 1 polymorphism and meat color and bone membrane color was observed (P < 0.05 ). This suggested that the mutation sequence may be involved in the regulation of the gene. The primer pair 2 polymorphism was caused by a A→G at nt -73 in the 5' flanking region upstream from the transcription initiation site of the gene, and a significant associations between the primer pair 2 polymorphism and stomach membrane color and bone membrane color was observed (P < 0.05 ). The third mutation was a T→C mutation found at nt 310 in code region. This mutation changed the codon TCC to CCC and revealed a missense mutation that replaces Ser to Pro at the 104th amino acid position. A significant associations between genotypes of this polymorphic site and stomach membrane color was observed (P < 0.05 ). This suggested that the mutation sequence may be influenced the structure of agouti-related protein. The fourth mutation was found at nt 480 in code region and changed the 160th codon TTC to TTT. But it is not cause the amino acid replace is a nonsense mutation. Chi-square test indicate this mutation is significantly related to skin color, meat color, bone membrane color and shank color.Because the process of melanogenesis was exceedingly complex, to absolutely elucidate the genetic effect of Agrp gene and TYR gene on the chicken color traits, the further study is necessary .