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Meiosis

Meiosis. Meiosis Meiosis Meiosis Meiosis. Defined : Process where the chromosome number is reduced by half Gametes created (egg & sperm) End Result : Four Haploid Cells. Interphase. Same process (G1, S, G2) Chromatin duplicated. Synthesis (S stage). Prophase 1.

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Meiosis

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  1. Meiosis

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

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

  4. Synthesis (S stage)

  5. Prophase 1 • Similar as mitosis, except… • Two Events: • 1) Synapsis: Pairing of homologous chromosomes • The four chromatids equal a TETRAD • 2) Crossing Over: Exchange of genes

  6. Early Prophase

  7. Synapsis: Homologous chromosomes align

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

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

  10. Telophase 1 • Cytokinesis divides the cells • Each cell contains 1 of the homologous chromosomes

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

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

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

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

  15. Spermato- genesis • Defined: Production of sperm cells • Occurs in male testes • Meiosis produces four haploid sperm cells at a time

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

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

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