罗非鱼链球菌病已成为制约罗非鱼产业发展的关键因素，目前仍无有效的防治方法。罗非鱼抗病品种(系)培育是防病的基础。而抗病力的分子遗传研究是抗病品种培育的前提。前期研究显示，尼罗罗非鱼抗病及感病群体之间MHCIIB基因多态性有着明显的差异；且MHC I基因cDNA有丰富的多态性。本项目拟进一步对尼罗罗非鱼MHC I 基因的基因组区域进行单核苷酸多态性（SNP）分析，利用SNP位点之间的连锁不平衡（linkage disequilibrium, LD），分析可能存在的单倍型块以及单倍型；进而分析单倍型块及单倍型上的标签SNP。利用标签SNP在抗病群体和感病群体中的分布频率的差异，判断其与抗链球菌病性能之间的关系，初步筛选链球菌病抗性/敏感相关单倍型或SNP位点；并在全同胞敏感和抗病个体中进行验证；最后通过分析它们的遗传特性及其在后代中的遗传分离模式和初步的辅助选育探讨其应用潜力。

The tilapia aquaculture industry has been severely threatened by S. agalactiae bacteria infection in recent years. It has not been found the effective prevention and treatment measures. The breeding of new stock with enhanced disease resistance is the foundation to prevent the disease. And the research of molecular heredity foundation of disease resistance is the premise of disease resistance breeding.The preliminary sutdies showed that there was a significant differences of MHC（major histocompatibility complex）IIB gene polymorphism between disease-resistant and susceptible groups in nile tilapia. And MHC class I gene cDNA has abundant polymorphism. In this study, the single nucleotide polymorphism (SNP) of MHC class I gene region will be analysed. The haplotype and haplotype block maybe exists in MHC class I gene region will be analysed using linkage disequilibrium method, and the tag SNP on the haplotype and haplotype block will also be analysed. The different distribution frequency of tag SNP and haplotype were used to estimate the relationship between tag SNP (haplotype) and disease resistance. Then the tag SNP or haplotype which correlate with resistance/susceptibility of streptococcus disease will be filtrated. The SNP or haplotype correlate with resistance/susceptibility of streptococcus disease will be tested in resistance/susceptibility individual of full-sibling family. The heredity characteristic and heredity segregation model of these SNPs or haplotype in offspring will be analysed. The application potential of these SNPs or haplotype will be discussed through primary assistant breeding.

罗非鱼链球菌病已成为制约罗非鱼产业发展的关键因素，目前仍无有效的防治方法。罗非鱼抗病品种(系)培育是防病的基础。而抗病力的分子遗传研究是抗病品种培育的前提。前期研究显示，尼罗罗非鱼抗病及感病群体之间MHCIIB基因多态性有着明显的差异；且MHC I基因cDNA有丰富的多态性。本项目进一步对尼罗罗非鱼MHC I 基因的基因组区域进行单核苷酸多态性（SNP）分析；对MHC IIA、B基因以及beta2m基因进行多态性分析。利用多态性等位基因在抗病群体和感病群体中的分布频率的差异，判断其与抗链球菌病性能之间的关系，初步筛选链球菌病抗性/敏感相关等位基因型或SNP位点；并在全同胞敏感和抗病个体中进行验证。这些与链球菌抗性和敏感相关的等位基因可以作为尼罗罗非鱼抗病选育的分子标记。建立了抗病F1家系39个，抗病F2家系74个，抗病F3家系42个。