中国明对虾第一代和第六代人工选育群体的遗传结构分析

Analysis of genetic structure in the first cultured stock and the sixth cultured stock of Fenneropenaeus chinensis

采用RAPD技术对中国明对虾(Fenneropenaeus chinensis)第一代和第六代人工选育群体的遗传结构及其分化进行了分析。在20个10bp随机引物中筛选出16个引物,共扩增出89条DNA片段,其中多态性片段分别为34和30条,多态位点比例分别为38.2％和33.71％。对2群体的遗传学参数计算结果表明:2群体间遗传分化指数为0.1408,属中等程度分化;群体间的遗传变异平均为0.197,由此可见,80％的遗传变异来自于群体内,而近20％的变异则是来自于群体间;第六代群体的多态位点比例和遗传多态度均低于第一代群体,这可能与人工定向选育过程中注重经济性状有关。

RAPD (Random Amplified Polymorphic DNA) technique was used to analyze the genetic structure and ge-netic differentiation of the first generation of cultured stock and the sixth generation of cultured stock of Fennerope-naeus chinensis. Genomic DNA was extracted from 40 samples for the two cultured stocks,anu PCR was performed in a 25 μL reaction mixture containing 20 ng genomic DNA,2.5 μL 10 PCR Buffer,2.0 mmol/L Mg2+ , l unit Tag DNA polymerase,0.2 mmol/L of each d NTP,and 0.6 mmol/L primer. PCR cycles were as follows:initial one step of 5 min at 94 ℃ ; subsequent 45 cycles of 1 min at 94 ℃ , 1 min at 37 ℃ , and 2 min at 72 8℃; followed by one final step of primer extension for 10 min at 72 ℃ . One negative control (absence of template DNA) was performed for each set of amplifications.PCR products were kept at 4 ℃ and isolated by electrophoresis on a 1.5% agar gel. The purpose of the study was to know the changes of genetic diversit.y in the successive cultured stocks of Fennerope-naeus chinensis in order to take effective measures such as marker-assisted selection to enable the sustainable develop-ment of the mariculture.Sixteen primers screened from 20 10-base primers yield 89 reproducible amplified fragments scored as present (1) or absent (0) for each DNA sample.Each primer used for the detection could produce 3-9 molecular markers varying in length from 250 bp to 2 000 bp. The polymorphic fragments of.the first generation of cultured stock and the sixth generation of cultured stock were 34 and 30, respectively, and the proportions of poly-morphic loci were 38.20% and 33.71% correspondingly. Genetic differentiation estimated using Nei's index be-tween the first stock and the sixth stock was 0.140 8, and the degree of genetic differentiation was moderate. The genetic diversities (H0) of the first generation of cultured stock and the six generations of cultured stock quantified by Shannon index were 0.212 and 0.184, respectively,indicating a low genetic diversity in the six generation of cultured stock. The ratio of Hpop/Hsp showed that the average genetic variability within stocks was 0.803, while the av-erage genetic variability among stocks was 0.197 that indicated 80% of genetic variability was from intra-stocks while about 20% of genetic variability was from inter-stocks. The lower value of genetic diversity and proportions of polymorophic loci in the sixth generation of the cultured stock may result from the selection based on the economic traits (e.g.better growth and disease resistance) . After selective breeding of six generations, the average body size and body weight of Fenneropenaeus chinensis in the cultured stocks increased significantly compared with control group.For example,compared with control the body size and body weight of Fenneropenaeus chinensis in the sixth generation of cultured stock increased by 8.40% and 28.60% ,respectively.