Genetic Diversity In Different Populations Of Tilapia (Oreochromis) By Microsatellite DNA Analysis

In this study,174 samples were collected from 6 tilapia populations:O. aureus("Xia Ao 1 Hao"), Egypt O. niloticus and 88 strain O. niloticus were cultured in Chinese Academy of Fishery Sciences Freshwater Fisheries Research Center; Guangxi O. aureus, Guangxi O. niloticus and America strain O. niloticus were obtained from Guangxi Institue of Fisheries. The two populations(ZA,ZN) which were introduced to Guangxi Institue of Fisheries were cultured in there, and formed another two populations(GA,GN). We extracted the gene group DNA using the method of phenol/chloroform. The genetic diversity of 25 microsatellite loci was analyzed with the microsatellite marker technology in the populations. The thesis discussed the genetic variation within population and among populations. Allele gene frequency, mean heterozygosisty, effective number of alleles, PIC, the Nei's standard genetic distance and DA genetic distance were calculated. Clustering dendrograms were obtained from Ds genetic distance. The results were as follows:1. The 25 microsatellite loci were selected and the results of the PCR in 174 samples of the 6 tilapia populations were got in every locus.143 alleles were tested in all the loci and the mean allelic number of per locus was 5.72. The efficient allelic number was 66.91. The efficient allelic number was less than the observed allelic number, which was the result of the alleles distributing unequally. The dominant allele was analyzed, and the results showed that the dominant allele was existed in all loci.2. The Hardy-Weinberg equilibrium analysis revealed that genetic disequilibrium was showed at four loci in 6 tilapia populations. Each locus in each population test showed that there were 8.11% loci in genetic disequilibrium. The reasons may be that the excursion occurred in random mating, the random genetic drift and breeding was existed in 6 populations. In those, the breeding was the main reason.3. The results showed that most of the 25 microsatellite loci had the high diversity, the mean polymorphic information content(PZC) value was between 0.404-0.6735, the mean polymorphic information contents of each population are from 0.4212 to 0.6105, which indicated that the 6 populations had moderate genetic diversity. The mean observed heterozygosisty was between 0.7253 and 0.8160, the mean expected heterozygosisty was between 0.5146 and 0.6834, and it showed that the six populations had higher heterozygosisty.4. The Nei's standard genetic distance and DA genetic distance among the six tilapia populations were estimated with the PopGenel.32 soft. The dendrograms were drawed with the Nei's standard genetic distances. The reault showed that the dendrogram of Ds genetic distance was similar with the origin, breeding and breeding intensity of the six tilapia populations. The six populations were clustered two groups. In the first group, Egypt O. niloticus and Guangxi O. niloticus clustered first, and then America strain O. niloticus, at last,88 strain O. niloticus was clustered with them. The O. aureus and Guangxi O. aureus were clustered another group.5. The F-statistic analysis indicated that the FST of different locus varied from 0.0779 (UNH738) to 0.3484(UNH183), and the average was 0.1937. The Nm was from 0.4675 to 1.8425, the mean was 1.0407.6. The Nei's standard genetic distance and FST values between Egypt O. niloticus and Guangxi O. niloticus were 0.1913,0.0904 respectively; the Nei's standard genetic distance and FST values between O. aureus and Guangxi O. aureus were 0.0911,0.0599 respectively. The result of AMOVA shows that:percentage of variation among populations within blue tilapia is 6.82%, percentage of variation among populations within Nile tilapia is 13.08%. There were not significant genetic differentiation parameters between introduced populations and original populations after generations of different artifical selections. O. aureus("Xia Ao 1 Hao") was cultured well in the other region in China; Egypt O. niloticus may need to be improved by different artifical selection.The result of cluster was consistent with origin, breeding and breeding intensity character of population. It was proved that DS and DA genetic distance were appropriate to microsatellite when used to reconstruct phylogenetic tree. The information about population genetic relationship estimated by microsatellite may be useful as an initial guide in evaluating the value of genetic variation, and developing conservation strategies.