Eight microsatellite DNA markers were used to assess genetic diversity of three generations of Litopenaeus vannamei, including a population imported from abroad (Go) and two cultured generations (G1 and G2 ). A total of 64 alleles were found in all eight loci with total alleles per locus ranging from 5 to 13 across the three generations. PIC ( Polymorphic Information Content) of the eight loci ranged from 0.405 2 to 0.869 3 with seven loci being highly polymorphic, which was useful for evaluating genetic variability. There were 30 alleles, including lost alleles and novel alleles, accounting for 47％ of all the alleles over the eight loci. The average observed heterozygosity of the Go, G1 and G2 generation were 0. 193 8, 0. 196 1 and 0.232 5 respectively, which suggested low genetic diversity of the three generations. Furthermore, inbreeding was observed through the three generations through Fis analysis. Significant deviations from HWE (HardyWeinberg equilibrium) for all tests at each locus and in each population were detected owing to homozygous deficiency. Pairwise Fst values and Nei's genetic distance showed obvious genetic differentiation among generations, which suggested obvious genetic variation of the population structure comparing filial generations with the original stock and the variance was probably derived from mutation, random drift and selection.Results could explain the exhibition of genetic characterization decline of the bred offspring prawns.Therefore, it is recommended that combined genetic breeding methods be adopted to select prawns of good and stable quality from imported parental stocks.%利用8个微卫星标记对引进的SPF凡纳滨对虾G1和两个养殖群体(G1,G2)进行遗传多样性分析.8个座位共获得64个等位基因,位点的等位基因数在5～13之间.多态信息含量PIC在0.405 2～0.869 3之间,其中有6个位点为高度多态位点,适合于多态性分析.8个座位丢失的和新产生的等位基因共30个,占总数的47%.3个群体的平均观测杂合度分别为0.193 8、0.196 1、0.232 5,说明3个群体的遗传多样性较低.对近交系数Fis分析显示3个群体中存在近交,通过对哈迪温伯格平衡检验,显示所有座位均显著偏离平衡,存在杂合子缺失.通过配对Fst和Nei遗传距离分析,显示3个群体之间有明显的遗传分化,说明种群结构发生了明显的遗传变异,变异可能来自于突变、随机漂变和选择的共同作用.实验结果能够很好地解释经过若干群体选育后,子代群体发生种质退化的现状,由此建议综合采用遗传育种的方法从引进的亲虾中筛选出性状优良稳定的仔虾作为虾苗.
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