Cell Division
Cell division is the process by which one parent cell divides to produce daughter cells. It underlies growth, tissue repair, and reproduction.
A. Mitosis
Mitosis Overview
- Produces 2 genetically identical daughter cells — same chromosome number as parent
- Daughter cells are diploid (2n) — in humans: 46 chromosomes each
- Occurs in somatic (body) cells — skin, muscle, liver, bone marrow
- Purpose: growth, tissue repair, and asexual reproduction
- One division cycle — PMATC (Prophase → Metaphase → Anaphase → Telophase → Cytokinesis)
Mitosis Result
1 parent cell (2n) → 2 identical daughter cells (2n)
No reduction in chromosome number. Genetically identical.
Phases of Mitosis — PMATC
| Phase | Key Events |
|---|---|
| Prophase | Chromosomes condense and become visible under microscope; nuclear envelope breaks down; spindle fibres begin to form from centrioles |
| Metaphase | Chromosomes line up at the cell's equator (metaphase plate); spindle fibres attach to centromeres. Longest phase. |
| Anaphase | Sister chromatids are pulled apart to opposite poles by spindle fibres shortening; cell elongates |
| Telophase | Nuclear envelopes reform around each set of chromosomes at poles; chromosomes decondense; two nuclei form |
| Cytokinesis | Cytoplasm divides — in animals: cleavage furrow; in plants: cell plate forms. Two daughter cells produced. |
⚡ Mnemonic Please Make A Tasty Cake — Prophase, Metaphase, Anaphase, Telophase, Cytokinesis
B. Meiosis
Meiosis Overview
- Produces 4 genetically different daughter cells — half the chromosome number
- Daughter cells are haploid (n) — in humans: 23 chromosomes each (gametes)
- Occurs in reproductive organs (gonads) — ovaries and testes
- Purpose: formation of gametes (sperm and egg cells) for sexual reproduction
- Two successive divisions: Meiosis I (separates homologous pairs) + Meiosis II (separates sister chromatids)
- Crossing over occurs during Prophase I — homologous chromosomes exchange segments, creating genetic variation
Meiosis Result
1 parent cell (2n) → 4 unique daughter cells (n)
Chromosome number halved. Each cell is genetically unique.
⚡ MCQ Tip Human body cells: 46 chromosomes (2n). After meiosis → gametes with 23 chromosomes (n). Fertilisation restores 46.
C. Mitosis vs Meiosis
Comparison Table
| Feature | Mitosis | Meiosis |
|---|---|---|
| Daughter cells produced | 2 | 4 |
| Chromosome number | Diploid (2n) — same as parent | Haploid (n) — half of parent |
| Genetic variation | None — cells are identical | Yes — crossing over creates variation |
| Number of divisions | One | Two (Meiosis I + II) |
| Where it occurs | Somatic (body) cells | Gonads (ovaries & testes) |
| Purpose | Growth, repair, asexual reproduction | Sexual reproduction (gamete formation) |
| Crossing over | Does not occur | Occurs in Prophase I |
| Example (humans) | Skin, liver, blood cells | Sperm and egg cells |
Quick MCQ Revision
| Fact | Answer |
|---|---|
| Mitosis produces | 2 identical diploid (2n) cells |
| Meiosis produces | 4 unique haploid (n) cells |
| Crossing over occurs in | Meiosis I (Prophase I) — creates genetic variation |
| Mitosis phases | PMATC — Prophase, Metaphase, Anaphase, Telophase, Cytokinesis |
| Chromosomes align at equator | Metaphase |
| Sister chromatids pulled apart | Anaphase |
| Human body cells | 46 chromosomes (23 pairs) — diploid |
| Human gametes | 23 chromosomes — haploid |
| Mitosis location | Somatic (body) cells — growth and repair |
| Meiosis location | Gonads — ovaries and testes |