Anaphase Promoting Complex (APC) is a protein degradation machinery necessary for proper mitosis of animal cells. If APC is defective in a human cell, which of the following is expected to occur?

Recombination of chromosome arms will occur

Which of the following options gives the CORRECT sequence of events during mitosis?

Condensation -> arrangement at equator -> centromere division -> segregation -> telophase

Condensation -> nuclear membrane disassembly -> crossing over -> segregation -> telophase

Condensation -> nuclear membrane disassembly -> arrangement at equator -> centromere division -> segregation -> telophase

Condensation -> crossing over -> nuclear membrane disassembly -> segregation -> telophase

Mitosis (M Phase)

மைட்டாசிஸ் (M நிலை)

NCERT Class 11 · Cell Cycle and Cell Division · 2 NEET questions

Do not mistake Mitosis for mere replication. It is the precise segregation of the genome into two identical nuclei. If the spindle fibers fail to attach at the kinetochore, you are looking at aneuploidy, not cell division.

The idea

M phase, or equational division, is the stage where the parent cell divides into two genetically identical daughter cells. It involves four distinct stages: Prophase, Metaphase, Anaphase, and Telophase. The process ensures the distribution of replicated chromosomes into daughter nuclei. Cytokinesis follows, completing the physical division of the cytoplasm.

Why it matters

It is essential for growth, tissue repair, and asexual reproduction, ensuring genetic continuity.

NEET lens

NEET focuses on the sequence of events and the specific changes in chromosomes during each phase. Memorize the behavior of the kinetochore and spindle fibers, as these are high-frequency questions. Do not confuse the equatorial plate alignment in Metaphase with the splitting of centromeres in Anaphase.

Clinical significance

Uncontrolled mitosis is the hallmark of malignancy. In cancer, the cell cycle checkpoints are bypassed, leading to rapid, unregulated proliferation of cells. This loss of mitotic control is why tumors grow exponentially.

Introduction

M phase (mitotic phase) is when cell division actually occurs, consisting of karyokinesis (nuclear division = mitosis) followed by cytokinesis (cytoplasmic division).

Core concept

M phase has two components: Karyokinesis = nuclear division with 4 stages: Prophase (chromosomes condense, spindle forms), Metaphase (chromosomes align at metaphase plate), Anaphase (centromeres split, chromatids move to poles), Telophase (nuclear envelope reforms). Then Cytokinesis = cytoplasm divides → 2 daughter cells. Cell cycle order: G1 → S (DNA replication) → G2 → M.

Go deeper

G2/M checkpoint: verifies DNA is fully replicated and undamaged before M phase begins. Spindle assembly checkpoint (SAC) during M phase: prevents anaphase until all kinetochores are attached to spindle microtubules. These checkpoints prevent catastrophic chromosome missegregation.

From Class 10

Cells divide to grow and reproduce. The actual division phase of the cell cycle — when the cell physically splits — is called M phase.