Apoptosis is a physiological process that occurs in cells during development and normal cellular processes, which eliminates the useless, unwanted, or damaged cells. Several markers are used to identify apoptosis in research such as the activation of caspases, the release of cytochrome C into the cytoplasm, and DNA fragmentation. Other characteristics including morphological changes, exposure of phosphatidylserine on cell surface, and change of mitochondrial membrane potential can also serve as the criteria for apoptosis identification.