10Class 11 Biology
Cell Cycle and Cell Division short notes
Short notes on the cell cycle, mitosis and meiosis. Questions often compare mitosis with meiosis, and ask about DNA and chromosome numbers at each stage.
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The cell cycle
- Interphase has G1 (growth), S (DNA doubles) and G2 (preparing for division).
- DNA doubles in S phase, but the chromosome number stays the same.
- Interphase takes up most of the cycle, and M phase is short.
- Cells that stop dividing enter G0, the quiescent stage.
Mitosis (somatic cells, equational)
- Prophase: chromatin condenses and the spindle begins to form.
- Metaphase: chromosomes line up at the equator, and this is the best stage to study their shape.
- Anaphase: centromeres split, and sister chromatids move to opposite poles.
- Telophase: nuclear envelopes re-form.
- Cytokinesis: a cleavage furrow in animal cells, and a cell plate in plant cells.
Meiosis (reproductive cells, reductional)
- Produces four haploid cells, which halves the chromosome number.
- Prophase I has five stages: leptotene, zygotene, pachytene, diplotene and diakinesis.
- Synapsis happens in zygotene, crossing over in pachytene, and chiasmata appear in diplotene.
- Homologous chromosomes separate in anaphase I, and sister chromatids separate in anaphase II.
Where students slip up
- Saying DNA doubling doubles the chromosome number. Chromosome number stays the same in S phase.
- Mixing up anaphase I and anaphase II, which separate different things.
- Forgetting the order of prophase I. A mnemonic helps: Lazy Zebras Prefer Dry Dirt.
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