Fluorescence in situ hybridization detected by tyramide signal amplification. Chromosome spreads were prepared from the cultured fibroblast cell line MRC-5 and hybridized with a biotinylated a-satellite probe specific for chromosome 17. The probe was generated by nick translation in the presence of ChromaTide® biotin-11-dUTP (Cat. no. C11411). For detection by TSA, hybridized chromosome spreads were labeled using TSA Kit #22 (Cat. no. T20932) with HRP–streptavidin and Alexa Fluor® 488 tyramide (upper panel) or with TSA Kit #23 (Cat. no. T20933) with HRP–streptavidin and Alexa Fluor® 546 tyramide (lower panel). After counterstaining with DAPI (Cat. no. D1306, D3571, D21490), images were obtained using filters appropriate for DAPI, FITC or TRITC.