Evaluation of the genetic diversity of microsatellite markers among four strains of Oreochromis niloticus.

Different strains of Nile tilapia can be found worldwide. To successfully use them in breeding programs, they must be genetically characterized. In this study, four strains of Nile tilapia - UFLA, GIFT, Chitralada and Red-Stirling - were genetically characterized using 10 noncoding microsatellite loci and two microsatellites located in the promoter and first intron of the growth hormone gene (GH). The two microsatellites in the GH gene were identified at positions -693 to -679 in the promoter [motif (ATTCT)8 ] and in intron 1 at positions +140 to +168 [motif (CTGT)7 ]. Genetic diversity was measured as mean numbers of alleles and expected heterozygosity, which were 4 and 0.60 (GIFT), 3.5 and 0.71 (UFLA), 4.5 and 0.57 (Chitralada) and 2.5 and 0.42 (Red-Stirling) respectively. Genetic differentiation was estimated both separately and in combination for noncoding and GH microsatellites markers using Jost's DEST index. The UFLA and GIFT strains were the least genetically divergent (DEST  = 0.10), and Chitralada and Red-Stirling were the most (DEST  = 0.58). The UFLA strain was genetically characterized for the first time and, because of its unique origin and genetic distinctness, may prove to be an important resource for genetic improvement of Nile tilapia. This study shows that polymorphisms found in coding gene regions might be useful for assessing genetic differentiation among strains.