Practice question

DAPI, 4',6-diamidino-2-phenylindole, binds strongly to the minor groove of double-stranded DNA with marked preference for AT-rich clusters. Upon binding, its fluorescence quantum yield increases more than twentyfold, emitting bright blue around 461 nanometers when excited by near-ultraviolet light. Because nuclei contain highly concentrated DNA, DAPI selectively highlights chromatin and chromosomes with low cytoplasmic background. It is membrane permeable for fixed cells, photostable, and compatible with green and red emitting markers for multi-color counterstaining of tissue sections, chromosome spreads and cell cycle analysis.