| The research takes 29 tilapia breeding families at Guangxi Nanning national tilapia seed multiplication farm in 2012 (including 12 U.S.type of oreochromis aureaus family and 17 U.S.type of Oreochromis niloticus family) as research object, uses microsatellite labeling technique, calculates the numbers of alleles (A), heterozygosity (H), polymorphism information content (PIC), genetic similarity coefficient (I), standard genetic distances (Ds), F statistic (F Stat) and gene flow (Nm) of each family, adopts standard genetic distances, uses MEGA3 software to build system dendrogram, and discusses the genetic diversity of each family, the genetic relationship and the genetic differentiation between families. The research results are as follows:1. Deal with PCR amplification to the mixture DNA of 10 individual of each family by using 20 pairs of tilapia microsatellite primers,114 alleles have been detected in 12 oreochromis aureaus families, and the allele number at each locus is within 1-9, the average value is 5.70. 147 alleles have been detected in 17 nile tilapia families, and the allele number at each locus is within 1-12, the average value is 7.35, and 14 pairs of primer used for family genetic background analysis have been picked out based on the amplification effect of each primer and number of alleles; and the effect of sample capacity to the numbers of alleles (A), heterozygosity (H) and polymorphism information content (PIC) of tilapia family has been analyzed by using 40 pairs of primer; showing that when sample capacity≥25, the genetic parameters average value change by getting is up to smooth and steady, and its reliability of the results is high. In order to research the accuracy and easy operation, this research will determine the volume of sample capacity as 30.2. It is shown from genetic diversity detection:the average value range of Ao, Ae, Ho, He and PIC in 12 oreochromis aureaus families are respectively 2.5000-2.9286,1.9164～2.3037, 0.4459-0.6171,0.3817-0.5051,0.3221-0.4324; the average value range of Ao, Ae, Ho, He and PIC in 17 Oreochromis niloticus families are respectively 2.6429-3.9286,1.9550-2.9439, 0.3884-0.7317,0.3979-0.6261,0.3478-0.5645, showing that the genetic diversity of oreochromis aureaus families is significantly lower than the genetic diversity of nile tilapia families. In general, two kinds of tilapia family are at a medium polymorphism level.3. It is shown from Hardy-Weinberg equilibrium test results:in 12 oreochromis aureaus families, the locus number of genotype frequency meeting Hardy-Weinberg equilibrium is 4-8, the average value is 5.5, the locus number of the highly significant(p<0.05) deviation from Hardy-Weinberg equilibrium is 4-6, the average value is 4.9167, the average value is 5.5, the locus number of the significant (p<0.05) deviation from Hardy-Weinberg equilibrium is 0-4, the average value is 1.5833, the locus number of singlet state is 0-4, the average value is 1.9167, respectively accounting for 39.29%,35.12%,11.31% and 13.69% of the total detection locuses; in 17 Oreochromis niloticus families, the locus number of genotype frequency meeting Hardy-Weinberg equilibrium is 3-7, the average value is 4.2353, the locus number of the highly significant (p<0.01) deviation from Hardy-Weinberg equilibrium is 3-11, the average value is 7.0, the average value is 5.5, the locus number of the significant (p<0.05) deviation from Hardy-Weinberg equilibrium is 0-4, the average value is 1.1176, the locus number of singlet state is 0-3, the average value is 1.4118, respectively accounting for 30.25%,50.00%%,7.98% and 10.08% of the total detection locuses. It can be seen that more than 50% of locus of each family are in the genetic imbalance state, while showing that the genetic equilibrium of above families has been broken.4. It is shown from the statistics of Nei’s standard genetic distance and genetic consistent degree that, the genetic distance of 12 oreochromis aureaus families is within 0.1617～0.5472, the genetic identity is within 0.5472-0.8507; the genetic distance of 17 Oreochromis niloticus families is within 0.1446～0.5660, the genetic identity is within 0.5678-0.8654. It is shown from Nei’s standard genetic distance data constructing system tree that, the genetic relationship gathered by two big teams between oreochromis aureaus family and nile tilapia is the farthest, and the intraspecific genetic relationship among families is the nearest.5. It is shown from F-statistics (Fis, Fit, Fst) and gene flow (Nm) calculation results:the values of Fis, Fit and Fst at each detection locus of oreochromis aureaus family are respectively within-0.5451～0.3429,-0.3578～0.6587 and 0.1153～0.6452, the mean values(average value) are respectively-0.2129,0.0957 and 0.2545, Nm value is within 0.1374-1.5009, the average value is 0.7325; the values of Fis, Fit and Fst at each detection locus of Oreochromis niloticus are respectively within-0.4553～0.7724,-0.2715～0.8529,0.1195～0.3535, the mean values are respectively-0.1479,0.1428 and 0.2532, Nm value is within 0.4572～1.8425, the average value is 0.7372. It is shown that the inbreeding pressure of groups is less, and the gene exchange frustration and genetic difference among various families are bigger.The development of this research has cleared the genetic diversity and genetic structure of 29 tilapia families, as well as the degree of genetic differentiation, and provided the molecular genetics reference for correctly evaluating breeding value of various families, the selection of backup parents, hybridization matching and other breeding operation. |
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