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11-4 Meiosis

11-4 Meiosis. Chromosome Number. Chromosomes are homologous Have one set from mother and one set from father Drosophila , a fruit fly, contains 8 chromosomes - 4 came from mother, 4 came from father. Chromosome Number.

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11-4 Meiosis

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  1. 11-4 Meiosis

  2. Chromosome Number • Chromosomes are homologous • Have one set from mother and one set from father • Drosophila, a fruit fly, contains 8 chromosomes - 4 came from mother, 4 came from father

  3. Chromosome Number • A cell that contains both sets of homologous chromosomes is diploid • Represented by 2N • For Drosophila, 2N = 8 • Body cells (i.e. skin cells, liver cells, etc.) • A cell that contains only one set of homologous chromosomes is haploid • Represented by N • For Drosophila, N = 4 • Sex cells - gametes (egg or sperm)

  4. The process that cuts the number of chromosomes in a cell by half Two Stages: Meiosis I Meiosis II Meiosis

  5. Chromosomes replicate Interphase I

  6. Chromosomes pair with homologous chromosomes to form a tetrad Contains 4 chromatids Chromatids cross-over Exchange portions of their chromatids Leads to genetic diversity Prophase I Tetrad Crossing Over

  7. Crossing Over

  8. Chromosomes line up in the center of the cell Spindle fibers form Metaphase I Spindle Fibers

  9. Homologous chromosomes separate Anaphase I

  10. Meiosis I ends with two haploid cells each with half the number of chromosomes as the original cell Telophase I and Cytokinesis

  11. It’s now time for Meiosis II!

  12. Chromosomes DO NOT replicate Start with two haploid cells each with half the number of chromosomes as the original cell Prophase II

  13. Chromosomes line up in the center of the cell Spindle fibers form Metaphase II

  14. Paired (sister) chromatids separate Anaphase II

  15. Results in 4 haploid (N) daughter cells Telophase II and Cytokinesis II

  16. Meiosis is how gametes are formed In males, gametes = sperm In female, gametes = eggs Gamete Formation

  17. Mitosis Starts with one diploid cell Cell divides once Occurs in 4 phases Results in 2diploid cells (all body cells) Cells are genetically identical Meiosis Starts with one diploid cell Cell divides twice Occurs in 8 phases Results in 4 haploid cells (gametes) Cells are genetically different Comparison of Mitosis and Meiosis

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