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)

When ionizing radiation hits a cell, DNA damage activates checkpoints that pause the cell cycle so repair can occur before mitosis. This pause that delays entry into mitosis is usually temporary because, if the damage can be repaired, the cell can resume the cycle and proceed to divide. This delay is most evident at moderate doses where repair is achievable, so the cell often returns to normal cycling. Only with severe, irreparable damage would cells fail to recover and may die or become permanently arrested, but that isn’t the typical outcome for a mitotic delay. Hence, the statement that radiation-induced mitotic delay is usually reversible best fits the biology.