THE GENETIC-STRUCTURE OF SEA BEET (BETA-VULGARIS SSP. MARITIMA) POPULATIONS - III - DETECTION OF ISOLATION BY DISTANCE AT MICROSATELLITE LOCI

Variation at three microsatellite loci was investigated in five popula tions of sea beet on the Dorset coast. Genetic variation among the pop ulations was estimated using two different methods. Estimates of F-ST were obtained using the program FSTAT, and estimates of R-ST were obta ined using the program AMOVA. These different estimates of genetic dis tance were used to test for isolation by distance with partial matrix correspondence tests and were compared with patterns of variation in F -ST estimates from isozymes and single-copy nuclear restriction fragme nt length polymorphisms (RFLPs). F-ST from isozymes, F-ST from RFLPs a nd R-ST from microsatellites all showed evidence of isolation by dista nce, whereas F-ST from microsatellites showed strong similarities with in populations that were not related to distance. These results sugges t that, compared with isozymes and RFLPs, mutation rates at microsatel lite loci are high in these populations. They also suggest that stepwi se mutation processes are occurring at these loci. The data provide va luable evidence that all three types of marker can detect similar patt erns of population structure. The results are discussed with respect t o estimates of genetic distance at microsatellite loci in human popula tions.