(1995). After the preamplification reaction, the reaction mixture was diluted to 150 μl with double distilled
H2O (dd H2O). The 10 μl PCR selective amplification system contained 1 μl of product from the diluted preamplification
reaction, 25 ng of both selective primers, 0.3 units of Taq DNA polymerase, 0.2 mM of each dNTP, 1.5 mM MgCl2 1X PCR buffer. All amplification reactions were performed in a Touch gene model thermocycler (Techne). Initially, three individuals from three studied strains were chosen to test the variation of 66 primer combinations (data not shown). With these individuals the polymorphism rates and the total number of bands with the 66 primer combinations were evaluated. The most useful primer combinations were considered those having the highest polymorphism rate that also
generate a reasonable number of clearly detectable total fragments. Using results from the evaluation of 66 primer combinations based on 3 individuals, the ten most-polymorphic primer combinations, producing clearly readable bands, were selected for the subsequent analyses with at least 30 samples. Gel analysis: An equal volume of loading buffer
(Formamide 10 ml, Xylene cyanol FF 10 mg, Bromophenol blue 10 mg, 0.5 M EDTA pH 8.0 200 μl) was added to each sample, and denatured at 95°C for 3 min then placed on ice for 2 min before loading. 4 μl of samples loaded onto 6% denaturing polyacrylamide gel matrix (7 M Urea; 19:1 Acrylamide: bis; 1X TBE buffer). The electrophoresis parameters were set to 75 Watt, 50°C and a run time of 1.5 hours was selected.Bands detected by the silver staining procedure
(Promega, Technical manual No.023) and gel images were scanned and saved as jpeg files for scoring and further
analysis. Two typical gels are shown in Figure 1a,b.