Ecotype variation at the 5S rDNA locus. FISH analyses of the 5S rDNA probe indicated signal variation between upland and lowland ecotypes. The upland tetraploid cultivars Dacotah (a) and Summer (b) were compared to the lowland tetraploid cultivars Kanlow (c) and Alamo (d). All FISH signals are of 5S rDNA, but both red and green fluorescence were used. White arrows in each image indicate “strong” signal patterns in comparison to “weak” signals in the same image (open arrowheads). The double “snake-eye” signal found in panel a simply indicates labeling of individual chromatids on the same chromosome. Scale bars = 5 μm.