What is Mitosis? — Definition, Types & NEET Biology

Mitosis — Explained for NEET

Mitosis is a part of the cell cycle that occurs during the M phase (mitotic phase). It is preceded by interphase, during which the cell grows and replicates its DNA. Mitosis itself is divided into four stages: prophase, metaphase, anaphase, and telophase, followed by cytokinesis.

During prophase, chromosomes condense and become visible, the nuclear membrane begins to disintegrate, the nucleolus disappears, and the mitotic spindle begins to form from centrioles (in animal cells). This is the longest phase of mitosis.

In metaphase, chromosomes align at the cell's equatorial plate (metaphase plate). Each chromosome is attached to spindle fibers at its centromere via kinetochores. This is the best stage to study chromosome morphology and count chromosome number.

Anaphase begins when centromeres split and sister chromatids separate, moving to opposite poles of the cell. This is the shortest phase of mitosis. The separated chromatids are now called daughter chromosomes.

During telophase, chromosomes reach the poles and begin to decondense. The nuclear membrane reforms, the nucleolus reappears, and the spindle fibers disintegrate. Telophase is essentially the reverse of prophase.

Cytokinesis (division of cytoplasm) occurs differently in plant and animal cells. In animal cells, a cleavage furrow forms and pinches the cell in two (centripetal). In plant cells, a cell plate forms at the center and grows outward (centrifugal).

Mitosis is significant for growth, repair of damaged tissues, and asexual reproduction. It maintains the chromosome number constant across generations of somatic cells.

Key Points from NCERT

• Mitosis produces two genetically identical diploid daughter cells — also called equational division
• Four stages: Prophase (longest) → Metaphase (chromosomes align at equator) → Anaphase (shortest) → Telophase
• Metaphase is the best stage for studying chromosome morphology and counting chromosome number
• Cytokinesis: cleavage furrow in animal cells (centripetal), cell plate in plant cells (centrifugal)
• Significance: growth, tissue repair, asexual reproduction, and maintaining constant chromosome number