Detection and analysis of DNA damage is of critical importance in a variety of biological disciplines studying apoptosis, cell cycle and cell division, carcinogenesis, tumor growth, embryogenesis and aging, neurodegenerative and heart diseases, anticancer drug development, environmental and radiobiological research, and others. Individual cells within the same tissue or in cell culture may vary in the extent of their DNA damage and, consequently, can display different reactions to it. These differences between individual cells in the same cell population are detected using in situ approaches. In situ is a Latin term meaning "on site" or "in place." It is used to denote the processes occurring or detected in their place of origin. In molecular and cell biology, this usually refers to undisrupted mounted cells or tissue sections. In that meaning, "in situ" is used as part of the terms.