Radiation-induced mitotic delay in the life cycle of a cell is:

• A. Usually irreversible
• B. Usually reversible
• C. Generally lethal to undifferentiated cells
• D. Both A and C

Answer: (B)

Radiation causes DNA damage, which triggers a checkpoint pause in the cell cycle to give the cell time to repair before mitosis. This mitotic delay is typically a temporary, reversible halt—most cells can repair the damage and later resume the cycle, moving into mitosis once the DNA is fixed. Only when damage is irreparable or repair fails would the cell progress die or undergo death pathways, but the delay itself is not inherently irreversible or fatal. The idea that this delay is generally lethal to undifferentiated cells doesn’t fit the mechanism of a reversible checkpoint arrest; the reversible nature of the delay best matches how cells usually respond to repairable radiation damage.