| 30 pairs of microsatellites primers derived from studied on Penaeus monodon, were used as common microsatellites primers in studied on marine shrimp Fenneropenaeus chinensis, Litopenaeus vannamei and Marsupenaeu japonicus. DNAs extracted from the 3 shrimp species were amplified by "Touchdown" PCR. 3 pairs of common microsatellites primers were screened and produced clear fragments. Optimal results were obtained by optimizing quantity of reagents and reaction conditions. Under the optima] conditions, PCR was performed for analyzing the genetic markers of the 3 species. As a result, clearly distinctive fragments were produced by the same microsatellites primers for the 3 species, which indicated that the genome of the 3 shrimp species have certain extents of comparability.Twenty-eight microsatellites primers were designed according to small-size fractionated genomic libraries of Fenneropenaeus chinensis. Of the 14 primers which PCR products could be detected by electrophoresis, five were polymorphic in mixed template (eight Chinese shrimp samples) by electrophoresis analysis. In these 5 microsatellites loci, genetic diversity was analysed in 20 Chinese shrimp samples from a cultured population by electrophoresis analysis, 4 microsatellites loci produced alleles numbered from 6 to 8, and the size of these alleles were from 142bp to 364bp, similar to their predicted size. The expected heterozygosity and the PIC values of them distributed from 0.7577 to 0.8064 and 0.7180 to 0.7709, respectively. These values showed that the 4 microsatellites loci could be applied for genetic diversity analysis on F. chinensis.Microsatellites technique was used to estimate genetics diversity and genetic structure of selected populations of F. chinensis, and the genetic divergency among populations also was studied. The main results are as follows:1. The genetic diversity of selected populations (CP1 and CP6) of F. chinensis were investigated. A total of 74 different alleles were derived from ten loci. The number of alleles per locus ranged from 3 to 13. PIC per locus ranged from 0.5567 to 0.8877. The average heterozygosity of the first and sixth selected generation were 0.6400 and 0.6300, respectively.Shannon genetic diversity index revealed that the average variation level of the two populations was 1.7742, and the variation level for the 1st and 6th selected generations were 1.6830 and 1.7382, respectively. Partitioning of the genetic variation revealed that 96.415% was distributed within populations and 3.585% among populations. Nei's genetic identity and genetic distance between the two populations were 0.9187 and 0.0848, respectively, which indicated low genetic differentiation between the two populations.2. Eight microsatellitess were used to study the genetic diversity of selected F. chinensis. A total of 71 alleles were found over all loci. The number of alleles per locus ranged from 6 to 16, with allele size ranging from 159 to 600bp. In all populations, the effective number of effective alleles was lower than the observed number (no). PIC (Polymorphism Information Content) per locus ranged from 0.6628 to 0.9051. The average heterozygosity of the 1 st, 3rd, 4th, 5th and 6th generation were 0.7188, 0.5687, 0.6188, 0.6438, and 0.66937, respectively. Shannon genetic diversity index revealed that the variation level was 1.8184, 1.8708, 1.7989, 1.7840, and 1.8095, respectively, with 1.9553 after pool data from the 5 generations as one population. Partitioning of the genetic variation revealed that 92.89% is distributed within populations and 7.11% among populations, which showed that most of the genetic variation was among populations. Genetic differences among the five populations were also detected based on the number of alleles per locus (no), the effective number of alleles , number of genotypes of per locus (G) , frequency of the most common allele (F), P values, F values and pairwise F values. The phylogenetic relationship among the five populations based on genetic distance were analyzed and shown by UPGMA dendrogra...
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