Q.Mitosis results in producing two cells which are similar to each other. What would be the consequence if each of the following irregularities occur during mitosis?
a. Nuclear membrane fails to disintegrate
b. Duplication of DNA does not occur
c. Centromeres do not divide
d. Cytokinesis does not occur.

Each of these four irregularities disrupts a different, specific step that mitosis normally relies on, so each has its own distinct consequence.

• a. If the nuclear membrane fails to disintegrate, the spindle apparatus forming in the cytoplasm cannot gain access to the chromosomes still enclosed within the nucleus, so the chromosomes cannot be captured at their kinetochores and moved to the metaphase plate — division is blocked from proceeding normally.
• b. If DNA does not duplicate, the cell would enter mitosis with chromosomes that have not doubled into two chromatids each, so there would be no equal, duplicated material to share between the daughter cells, and the resulting cells would not receive a complete, matching set of chromosomes.
• c. If centromeres do not divide, the sister chromatids of every chromosome cannot be separated at anaphase, so the chromosomes cannot be pulled apart to the two poles and nuclear division cannot be completed correctly. …

Mitosis depends on several separate steps happening correctly and in sequence, and each of the listed irregularities strikes at a different one of them:

• a. Nuclear membrane fails to disintegrate. Normally, the complete disintegration of the nuclear envelope marks the onset of metaphase, freeing the chromosomes so they can be reached and captured by spindle fibres coming from the cytoplasm. If the envelope stayed intact, this access would never happen — the spindle apparatus, built in the cytoplasm from the two asters and their fibres, would have no way to attach to the chromosomes' kinetochores, and the chromosomes could never be drawn to the metaphase plate or separated. Division would essentially stall at this point.

• b. Duplication of DNA does not occur. DNA replication in S phase is what turns each chromosome into a pair of identical sister chromatids joined at a centromere. Without this doubling, the cell would carry only single-stranded (unduplicated) chromosomes into mitosis. There would be nothing equal to share out between two daughter cells — either the division could not proceed as normal, or it would produce daughter cells with an incomplete or unequal share of genetic material rather than each daughter receiving a full, faithful copy. …

Step 1 — For each irregularity, identify the normal step it disrupts and trace the direct consequence.

Step 2 — a. Nuclear envelope not disintegrating → the spindle apparatus (built in the cytoplasm) can't reach chromosomes still enclosed in the nucleus → division blocked from proceeding normally.

Step 3 — b. No DNA duplication → chromosomes enter mitosis single-stranded (unduplicated) → no equal, duplicated material exists to distribute to two daughter cells. …