Abstract: B-G gene of the MHC families is related to the traits of disease resistance in chicken breeds. Investigation on the polymorphism of B-G genes can fundamentally improve the chickens disease resistance， and then lay a foundation for resistance breeding. In this study， the DNA samples of 25 chicken breeds were used by target capture sequencing method for gene sequencing. Considering B-G gene sequence of Gallus gallus as the reference， we used MEGA6 software for gene analysis to seek out single nucleotide polymorphism (SNP)， insertiondeletion (Indel) and the changes of amino acid， and finally constructed the evolutionary tree. The results revealed that exons had 8 SNPs， 19 Indels and introns had 67 SNPs， 327 Indels in 25 chicken breeds. Amino acids also presented certain polymorphisms and local breeds showed high degree of genetic diversity. This method provided abundant B-G genotypes in the chickens， such as recessive white chicken， Xianju chicken， Leghorns chicken. Leghorns chicken was in separate evolutionary tree for category. Tibetan chickens and Wenchang chickens were also separately categorized due to the geographical location factor. Rose in modern poultry and recessive white chickens gathered for one class， but homology between different types of Chinese local breeds were smaller. The above experiments showed that there were several origins and plenty of genetic diversities of B-G gene， which resulted in different disease resistance in Chinese indigenous breeds.

Key words: chickens, BG gene, SNPs, Indels, phylogenetic tree