MICROSATELLITE POLYMORPHISM IN NATURAL-POPULATIONS OF THE WILD PLANT ARABIDOPSIS-THALIANA

Variation in repeat number at 20 microsatellite loci of Arabidopsis th aliana was studied in a worldwide sample of 42 ecotypes to investigate the pattern and level of polymorphism in repetitive sequences in natu ral plant populations. There is a substantial amount of variation at m icrosatellite loci despite the selfing nature of this plant species. T he average gene diversity was 0.794 and the average number of alleles per locus was 10.6. The distribution of alleles was centered around th e mean of repeat number at most loci, but could not be regarded as nor mal. There was a significantly positive correlation between the number of repeats and the amount of variation. For most loci, the observed n umber of alleles was between the expected values of the infinite allel e and stepwise mutation models. The two models were rejected by the si gn test. Linkage disequilibrium was detected in 12.1% of the pairwise comparisons between loci. In phylogenetic tree, there was no associati on between ecotype and geographic origin. This result is consistent wi th the recent expansion of A. thaliana throughout the world.