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DNA fragmentation in human sperm as determined by TUNEL assay. A) Fluorescence microscopy images of sperm derived from men in (a) the fertile normozoospermic group (control), (b) asthenozoospermic (AST) group, and (c) oligoasthenoteratozoospermic (OAT) group. White arrows indicate TUNEL-positive nuclei (bright green), while DAPI (blue) staining indicates the total number of nuclei (scale bar: 50 µm). B) Quantitative determination (percentage of apoptotic cells versus the total number of cells) of DNA fragmentation in sperm of males in the control, AST, and OAT groups. A greater number of TUNEL-positive nuclei were observed in the OAT and AST groups than in the control group