Scission of the chromatin at the sites of nucleosomal linkage creates a large number of strand breaks in the DNA of apoptotic cells. The broken ends can be labelled enymatically in situ by terminal deoxynucleotidyl transferase (Tdt).
The ends of DNA can be labelled directly using fluorescein-deoxyuridine triphosphate (dUTP) or biotin-dUTP followed by fluorescein-streptavidin or digoxygenin-dUTP followed by fluorescein-anti-digoxygenin.
