Lecture Notes: Meiosis I and Meiosis II; Life Cycles

Overview of Meiosis

• Purpose: Reduces the number of chromosomes by half, essential for sexual reproduction.
• Outcome: Each daughter cell has half the number of chromosomes compared to the parent cell.
• Relevance: Forms gametes (sperm and eggs) which are haploid (N), unlike diploid (2N) somatic cells.

Divisions of Meiosis

• Meiosis I:
  • Cells double but chromosome count is halved.
  • Phases: Prophase I, Metaphase I, Anaphase I, Telophase I.
• Meiosis II:
  • Similar to mitosis, no reduction in chromosome number.
  • Phases: Prophase II, Metaphase II, Anaphase II, Telophase II.

Detailed Phases of Meiosis

Meiosis I

1. Prophase I
   • Similar events to prophase in mitosis.
   • Chromosomes coil; nuclear membrane disintegrates.
   • Chromosomes may undergo "crossing over," exchanging fragments.
2. Metaphase I
   • Bivalents (tetrads) align in the cell's center.
   • Involves independent assortment—random arrangement of chromosome pairs.
3. Anaphase I
   • Homologous chromosomes separate.
4. Telophase I
   • Nuclear envelope reforms, nucleoli reappear.

Meiosis II

5. Prophase II
   • Chromosomes coil, nuclear membrane disintegrates.
6. Metaphase II
   • Spindle fibers form; sister chromatids align at cell equator.
7. Anaphase II
   • Sister chromatids separate.
8. Telophase II & Cytokinesis II
   • Chromatids uncoil into chromatin.
   • Nuclear membrane reforms, resulting in 4 haploid (N) daughter cells from 2 diploid (2N) cells.

Additional Resources

• Works Cited
  • Genetics Suite, Jolly, R. L. D., and Meiosis resources for further study.
  • Diagrams and images available for visual reference of phases and chromosome numbers.

Diagram Labeling

• Label diagrams with phase or cell type and chromosome number.
• Important for visualizing the transition through meiotic phases.