Study On The MHC Class I Gene Polymorphism Of Four Pochard Ducks In China

The adults of Aythya baer is fewer than 1000,it is one of the world 's most endangered birds and its population is severely threatened.Major histocompatibility complex is one of the most polymorphic genes in vertebrates,it plays an important role in immune defense against pathogens,The polymorphism of MHC can reflect a species' ability to adapt to the environment.The aim of this study was to investigate the mechanism of maintaining the polymorphism of MHC I genes in Aythya baeri,Aythya marila,Aythya fuligula and Aythya ferina.We research through the nine Aythya baeri,nine Aythya marila,eight Aythya fuligula,and ten Aythya ferina Which are 36 individuals MHC I gene sequences,after we screened 720 clones,a total of 102 alleles were obtained.The Aythya baeri,Aythya marila and Aythya ferina single out 24 alleles.The Aythya fuligula find out 30 alleles,then we firstly get the name of them.Based on the analysis of base composition proportion,the base composition of Aythya baeri is similar with the Aythya marila,the base composition of Aythya fuligula is the same with Aythya ferina.We also found GAG(E),GUG(V),and CAG(Q)were the top three codons in exon2,GAG(E)?GAC(D)? GGG(G)or AAG(K)were top three codons in exon3 of the four Chinese Aythya.Elective pressure analysis showed that the d N/d S of ABS which are bound to antigens is subject to positive selection,while purifying selection was detected in regions that were not bound to antigens.The M8 model of PAML was used to detect the selected sites of exon 2 and 3 in the four Chinese poached duck.Most of the selected sites were located in the ABS region that binds with antigen.Through phylogenetic trees constructed by exons 2 and 3,we found that there is cross-species evolution between MHC ? genes of Aythya species.Recombination signals and breakpoints were detected in all four Chinese poached duck.The above analysis shows that balanced selection and recombination play an important role in maintaining the diversity of MHC ? genes in four Aythya.