Genotype frequency contributions of Mx1 gene in eight chicken breeds under different selection pressures.

Chicken Mx1 gene, as a positive antiviral gene, has been reported to provide resistance to several viruses especially avian influenza virus. In present research, the genotype frequency contributions of chicken Mx1 polymorphisms were characterized in five lowly selected as well as one moderately selected Sichuan native chicken populations and two highly selected commercial chicken breeds. Together with two newly-identified mutation sites (r.8A > G and r.1257T > C), a total of 13 single nucleotide polymorphisms (SNPs), including seven nonsynonymous mutation and six synonymous mutation, were found in the coding region of chicken Mx1 gene. Local Chinese chicken populations exhibited higher nucleotide diversity than commercial populations. Moreover, amino acid substitution sites as well as positive selection sites were located only in the domain not determined and GTPase domain, implying that amino acids mutations were likely needed in the modulatory and structural regions to better adapt the environment. Collectively, our results suggest that different selection pressures greatly influenced the genotype frequency contributions of chicken Mx1 gene. Understanding the interaction between genetic diversity and artificial selection may help us to better select and breed superior domestic chickens.