Fluorescence in situ hybridization of repetitive probes onTetraodon nigroviridis metaphase chromosome. (A) A cloned 180-bp fragment of the 118-bp satellite hybridizes uniformly to all centromeres. Fluorescein isothiocyanate signals are in green, and chromosomes are counterstained with DAPI. (B) A synthetic probe that includes 4 consecutive monomers of the 10 bp satellite labels specifically the short arms of 10 pairs of subtelocentric chromosomes. Fluorescein isothiocyanate signals are in yellow, and chromosomes are counterstained with DAPI and PI. Arrows indicate the 11th pair of subtelocentric chromosomes that carries the 18S-5.8S-28S rRNA gene clusters and which is strongly stained with propidium iodide.