Number of occurrences of simple sequence repeats in D. purpureum and D. discoideum genomes. (a,b) The numbers of repeats were classified by the length of repeat tracts (a) and the length of repeat units (b). The D. purpureum genome (circles) has fewer and shorter microsatellites than the D. discoideum genome (triangles) in both coding regions (solid circles and triangles, and solid lines) and non-coding regions (open circles and triangles, and dashed lines). Not shown are three D. discoideum repeats above 250 nucleotides in (a). The minimum number of repeats of the unit motif was 10 repeats for mononucleotides, 7 repeats for dinucleotides, 5 repeats for trinucleotides, 4 repeats for tetranucleotides, 3 repeats for pentanucleotides and longer (6- to 20-nucleotide) motifs.