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Meiosis

Meiosis. Quick review: identify this stage of the diploid cell cycle. Prophase. Quick review: identify this stage of the diploid cell cycle. telophase. Quick review: identify this stage of the diploid cell cycle. anaphase. Quick review: identify this stage of the diploid cell cycle.

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Meiosis

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  1. Meiosis

  2. Quick review: identify this stage of the diploid cell cycle. Prophase

  3. Quick review: identify this stage of the diploid cell cycle. telophase

  4. Quick review: identify this stage of the diploid cell cycle. anaphase

  5. Quick review: identify this stage of the diploid cell cycle. metaphase

  6. Quick review: identify this stage of the diploid cell cycle. interphase

  7. Meiosis Meiosis Meiosis Meiosis • Defined: Process where the chromosome number is reduced by half • Gametes created (egg & sperm) • End Result: Four Haploid Cells

  8. Interphase • Same process (G1, S, G2) • Chromatin duplicated

  9. Synthesis (S stage) Chromatin strands duplicated

  10. Prophase 1 • Similar as mitosis, except… • Two Events: • 1) Synapsis: Pairing of homologous chromosomes • Dad’s #1 chromosome pairs with Mom’s #1, etc… • The four paired chromatids equals a TETRAD • 2) Crossing Over: Exchange of genes

  11. Early Prophase Chromosomes form Nucleus dissolves

  12. Synapsis tetrad tetrad Spindle fibers pull homologous chromosomes together tetrad

  13. Metaphase 1 • Homologous chromosomes (tetrads) align along cell equator

  14. Anaphase 1 • Homologous chromosomes are pulled apart to opposite ends • Tetrads separated

  15. Telophase 1 • Each cell contains 1 of the homologous chromosomes • In humans = 23 chromosomes • Cytokinesis divides the cells

  16. Prophase 2 • Same as mitosis • Note: No new DNA was created (no 2nd interphase)

  17. Metaphase 2 • Remaining chromosomes are aligned at cell equator

  18. Anaphase 2 • Sister chromatids are pulled to opposite ends

  19. Telophase 2 • Nucleus reforms on the four new cells • Chromatids uncoil • Cytokinesis divides the cells • End Result: Four haploid cells

  20. Spermatogenesis Meiosis 1 • Defined: Production of sperm cells • Occurs in male testes • Meiosis produces four haploid sperm cells at a time Meiosis 2 Spermatogenesis

  21. oocyte Oogenesis Meiosis 1 • Defined: Production of the egg cell (ovum) • During meiosis I: Cytoplasm distributed unequally • After meiosis II: • 1 cell matures • 3 “Polar Bodies” dissolve Meiosis 2 Oogenesis

  22. Division of somatic cells Ex: Blood cells, skin cells, nerve cells… End Result: 2 Diploid Cells (2n) Importance: Replaces aging cells Importance: Form of asexual reproduction Division resulting in gametes Ex: Sperm and Egg cells End Result: 4 Haploid cells (n) Importance: Reduces the gamete chromosome number by half Mitosis Meiosis

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