Essential Key Points: Mitosis
1. Definition and Purpose Mitosis = equational division. One diploid (2n) parent → 2 diploid (2n) identical daughters. Used for: growth of organisms, repair of tissues, asexual reproduction. Occurs in somatic (body) cells.
2. Prophase
- Chromatin condenses → visible chromosomes (each = 2 sister chromatids joined at centromere)
- Nucleolus disappears (rRNA transcription halts)
- Mitotic spindle begins to form (from centrioles in animal cells; MTOCs in plant cells)
- Nuclear envelope still intact (breaks in prometaphase)
3. Metaphase
- Chromosomes align at metaphase plate (equatorial plane)
- Kinetochores on centromeres attach to spindle fibres from opposite poles (amphitelic attachment)
- Chromosomes are maximally condensed — best stage for karyotyping
- Colchicine blocks tubulin polymerisation → arrests cells here
4. Anaphase
- Centromeres split → sister chromatids become individual chromosomes
- Chromosomes pulled to opposite poles by shortening kinetochore microtubules
- Chromosome count transiently doubles: 2n → 4n in the cell (resolves after cytokinesis)
- Cell elongates due to polar microtubule elongation
5. Telophase
- Chromosomes arrive at poles and decondense
- Nuclear envelope reforms around each chromosome set
- Nucleolus reappears as rRNA transcription resumes
- Followed immediately by cytokinesis
6. Cytokinesis: Animal vs Plant
| Feature | Animal Cells | Plant Cells |
|---|---|---|
| Structure | Cleavage furrow | Cell plate |
| Direction | Centripetal (outside → centre) | Centrifugal (centre → outside) |
| Components | Actin-myosin contractile ring | Golgi-derived vesicles |
| Mechanism | Plasma membrane pinches inward | Vesicles fuse to form new wall |
7. Key Differences: Plant vs Animal Mitosis
- Animal cells have centrioles and asters (astral microtubules); plant cells lack both
- Plant cells have anastral spindle (no asters)
- Cytokinesis mechanism differs entirely (as above)
8. Products of Mitosis
- 2 cells, each genetically identical to parent
- Chromosome number: 2n (maintained)
- DNA content: 2C (restored after halving from 4C)
- Genetically IDENTICAL to each other and the parent
9. Mnemonic PMAT = "Please Make Another Taco"
- Prophase = Prepare (condense, spindle forms)
- Metaphase = Middle (align at middle plate)
- Anaphase = Apart (chromatids move apart)
- Telophase = Two (two nuclei form)