FISH analyses of switchgrass chromosomes. Comparative FISH analysis of switchgrass chromosomes was conducted using four different probe sequences: CentC (a,b,c); PviCentC (d,e,f); 45S rDNA (g,h,i); 5S rDNA (j,k,l). Three different switchgrass cytotypes were analyzed for each FISH probe: dihaploid 2n = 2X = 18 (a,d,g,j); tetraploid 2n = 4X = 36 (b,e,h,k); octoploid 2n = 8X = 72 (c,f,i,l). CentC signals (a,b,c) are indicated in green, whereas all other probes are labeled with red fluorescence. White arrows in d, e, and f indicate the strong PviCentC signal present on Chromosome 3 of the basic karyotype (n = 9). White arrows in k and l indicate “strong” 5S rDNA signals as compared to the “weak” 5S rDNA signals in each image (open arrowheads). Scale bars = 5 μm.