Chromosomal distribution of the mono- and dinucleotide SSRs in the salivary gland (a, d, e, and h) and neuroblast cells (b, c, f, i and j) of D. melanogaster after ND-FISH and DAPI staining. Both polytene chromosomes and diploid nuclei are shown in g; examples of two-colour ND-FISH with (AAGAG)5 are shown in h (insets) and j. Each panel shows individual and/or merged images to facilitate the appreciation of the distribution of signals (green or red from digoxigenin- and biotin-labelled probes respectively) and identification of chromosomes. The localization of the signals with respect to the heterochromatic DAPI banding pattern in mitotic chromosomes is shown in Figure 4. Note the high concentration of A, C, AC and AG SSRs on polytene X chromosomes; this contrasts with the lesser presence of these repeats on chromosome 4. An enlarged view of the A repeat signals at the base of chromosome X (square) and chromosome 4 is shown at the right of panel a. The arrows point chromosomes 4; CR, chromocentre. Scale bar = 5 μm and 25 μm in (pro)metaphase and polytene nuclei respectively.