Q.48 Under which of the following conditions, a mammalian somatic cell fails to
undergo mitosis during cell cycle?
(A) Initiation of cell plate formation
(B) Incomplete DNA replication
(C) Chiasmata formation
(D) Irreparable DNA damage

Mammalian somatic cells halt mitosis to prevent genomic instability from errors like incomplete replication or damage. The correct answer is (D) Irreparable DNA damage, as checkpoints block progression to avoid propagating mutations.​

Correct Answer

D) Irreparable DNA damage

Irreparable DNA damage triggers the G2/M checkpoint, activating p53 and halting cyclin B-CDK1 activity to prevent mitosis entry. This ensures cells with severe damage undergo apoptosis or senescence instead of faulty division.​

Option Explanations

A) Initiation of Cell Plate Formation

Cell plate formation occurs in plant cytokinesis, not mammalian somatic cells, which use cleavage furrow via actin-myosin. It follows mitosis completion and does not inhibit the process.​

B) Incomplete DNA Replication

Incomplete DNA replication activates the S-phase or G2 checkpoint, delaying but not always preventing mitosis entry; cells may proceed with replication forks unresolved, risking errors.​

C) Chiasmata Formation

Chiasmata form during meiotic prophase I for recombination, absent in mitotic somatic cells where homologous chromosomes do not pair. No role in blocking mitosis.​

D) Irreparable DNA Damage

Severe, uncorrectable DNA damage (e.g., double-strand breaks) engages DNA damage response pathways, enforcing G2 arrest via ATM/ATR kinases to block mitotic entry.​

Cell Cycle Checkpoints Table