中国部分地方鸡种MHC B-G基因第二外显子的遗传多态性  

Genetic polymorphism within exon 2 of MHC B-G gene in nine Chinese indigenous chicken breeds

作　　者：徐日福[1] 李奎[1] 陈国宏[2] 强巴央宗[3] 张玉波[1] 林丽[1] 樊斌[1] 刘榜[1] 

机构地区：[1]华中农业大学动物科技学院 [2]扬州大学动物科技系,江苏扬州225009 [3]西藏大学农牧学院畜牧兽医系,西藏林芝860000

出　　处：《动物学报》2006年第1期160-169,共10页ACTA ZOOLOGICA SINICA

基　　金：引进国际先进农业科学技术项目"948"(No.2001361);国家重点基础研究发展规划项目(No.G2000016103)~~

摘　　要：根据鸡主要组织相容性复合体BG基因序列设计特异性引物,在9个中国地方鸡种和1个国外引进鸡种基因组中扩增了包括其第一内含子和第二外显子在内、长度为401bp的DNA片段。经PCRSSCP分型筛选后,对该片段的核苷酸序列进行克隆测序和直接PCR测序及比对分析,发现了31个MHCBG新等位基因;各等位基因主型所含有的亚型数及其在不同品种间的分布极不均衡。第二外显子核苷酸序列和其所编码的MHCBG抗原类IgV结构域氨基酸序列比较表明,在中国地方鸡种BG基因第二外显子的207bp序列中有37个多态性变异位点,其中简约性信息位点29个,单个位点的变异8个;等位基因间的遗传变异范围0.0013-0.1433;各变异位点的核苷酸变异指数0.206-1.462。该编码区核苷酸的异义替换率为9.26%±1.92%,高于同义替换率2.34%±0.90%。所估计的核苷酸转换数和颠换数随着遗传距离的增加而逐渐增加,当核苷酸转换数和颠换数达到平衡后,该片段核苷酸转换数的增加幅度逐渐高于颠换数。在其所编码的类IgV结构域氨基酸序列中,多态变异位点有22个,其中简约性信息位点6个,单变异位点16个;所估测的等电点为8.45,疏水性氨基酸占40.3%,亲水性氨基酸占29.9%;该序列具有明显的疏水性特点。等位基因间的系统发生分析表明,31个BG等位基因分为两个群,相同主型的等位基因首先聚类。Genetic polymorphism within chicken major histocompatibility complex B-G genes was investigated by amplification of exon 2 using PCR, followed by cloning and DNA sequencing after preliminary screening on 557 individuals from nine Chinese indigenous breeds and one exotic breed. We found 31 novel alleles of B-G genes,and allele distributions at the different breeds were notably non-symmetrical. Alignment and comparison of the 29 sequences from Chinese local chickens revealed a total of 37 variable sites in the fragment of exon 2, of which 29 parsimony informative and 8 singleton variable sites were observed. The genetic distances between the alleles were estimated, 0.0013-0.1433;the variation index for per variable site was calculated as the entropy of 0.206-1.462.The relative frequencies of non-synonymous substitutions of nucleotide per non-synonymous site and synonymous substitutions per synonymous site within the region were 9.26%±1.92% and 2.34%±0.90%, respectively. The number of observed transitions versus tranversions gradually increased with genetic distances, indicating that the nucleotide substitution in the region was not saturated. Alignment of deduced amino acid sequences encoded by exon 2, showed 22 polymorphic sites of which 6 sites were parsimony informative and 16 sites were singleton variable. The amino acid properties of the immunoglobulin variable-like domain along the sequence were investigated. Its isoelectric point was 8.45, and hydrophobic amino acids accounted for 40.3% and hydrophillic 29.9%. Investigation of the dendrogram constructed using the sampled sequences revealed a preliminary phylogeny among the 29 alleles from the Chinese native chicken populations. It provided molecular data for the study on immune function and genetic evolution of chicken B-G gene

关 键 词：中国 地方鸡种 B—G基因 等位基因 遗传多态性 

分 类 号：S831[农业科学—畜牧学]