Polymorphism Of Exon 2 Of MHC Class Ⅱ DRB Gene In Sable (Martes Zibellina) In Northeast China

Martes zibellina is a precious small mammal that belongs to the Mustelidae.It can be divided into several categories depending on the habitats and characteristics:the Martes zibellina altaica;the Martes zibellina princeps;the Martes zibellina linkouensis and the Martes zibellina hamgyenensis.Due to the land reclamation and deforestation,the habitat shrankrapidly;and they were killed for their valuable fur,which made them get less.Major histocompatibility complex(MHC)is one of the most polymorphic genes in vertebrates.The MHC molecules respond to species’ ability to adapt to the environments,it partly reflects the historical events of the species,thus it becomes an effective molecular marker for the study of genetic evolution of species.This study focuses on sable MHC class Ⅱ DRB gene exon 2.According to the studies of 25 sable individuals MHC class Ⅱ DRB gene exon 2,we had found 28 DRB exon 2 alleles and 9 pseudogenes for the first time;In the base composition,28 alleles are rich in CG and make up 62.1% of all base pairs,the high content of CG is closely related to maintaining the normal function of genes;In amino acids,the DRB exon 2 gene encodes 80 amino acids,and the mutation sites have 30,accounting for 37.5%.Among the amino acids that make up the DRB exon 2,the highest average utilization rate was Glutamate(10.625%)and Arginine(10.982%),and the lowest was Methionine(0.625%)and Isoleucine(0.759%).In terms of codons usage,the top three users with the highest utilization rate were GAG(8.5 times),GUG(6.8 times)and UUC(5.6 times).We used MEGA5 software(based on Nei-Gojobori method(Jukes-Cantor)model)to calculate the PBR and non-PBR sites of synonymous substitution rate and non synonymous substitution rate;From the PBR sites,d N/d S > 1,the gene suffered positive selection;From the non-PBR sites,d N/d S<1,the gene did not suffer positive selection;From all sites,d N/d S>1,the gene is under positive selection.The genetic distance between the 28 allele sequences was between 0.004 and 0.193,with an average genetic distance of 0.092.By analysing the Bayesianphylogenetic tree we know that the gene may have trans-species polymorphism.