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Mitosis vs. meiosis

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Ch. 8 Modern Biology Section3 - Meiosis
differentiate between mitosis and meiosis

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Mitosis vs. meiosis

  1. 1. Mrs. Stewart Biology I standard
  2. 2. REVIEW:  Cell Cycle  Interphase  G1, S, and G2  M-phase (mitosis)  P-M-A-T-C  Mitosis  Asexual reproduction  Produces 2 identical daughter cells  Daughter cells are diploid  Daughter cells are identical to parent/mother cell
  3. 3. What differences can you see? • How many sets of chromosomes are in the cells that Meiosis produces? • How many cells does Meiosis produce? • How many divisions occur in Meiosis?
  4. 4. Final Products: Mitosis Somatic cells in your body have two sets of chromosomes they are called DIPLOID Meiosis Gametes (Sex cells-sperm and eggs) only have one set (half) of chromosomes - they are called HAPLOID
  5. 5. MEIOSIS:  The process of creating a gamete
  6. 6. What are the steps?  Phases of Meiosis I  Prophase I  Metaphase I  Anaphase I  Telophase I  Cytokinesis  Interkinesis  Phases of Meiosis II  Prophase II  Metaphase II  Anaphase II  Telophase II  Cytokinesis
  7. 7. Let’s see it in action!  Meiosis animation
  8. 8.  DNA replicates Interphase  Makes the diploid (2n) cell now be (4n)  n=number of chromosome sets/pairs  Example: humans have 46 total chromosomes, so our diploid number is 2n or 2(23) where n = 23
  9. 9. Chromosomes come in matching sets -these are called homologous pairs
  10. 10. Karyotype after DNA replication Notice how each chromosome has duplicated itself.
  11. 11. Prophase I • Homologous chromosomes pair up (forming a tetrad) - Mom & Dad go on a date • Crossing over occurs • Chromatids MAY exchange portions of DNA • Leads to genetic variances
  12. 12. Prophase I  Homologs (homologous pairs of chromsomes) form Tetrads  Crossing Over occurs
  13. 13. Metaphase I  Spindle fibers attach to the chromosomes  Homologous chromosomes line up in the middle of the cell Anaphase I • Fibers pull the homologous chromosomes toward opposite ends of the cell Telophase I and Cytokinesis • Nuclear membranes form • Cell separates into two new cells
  14. 14. Interkinesis  Resting period between Meiosis I and Meiosis II  DNA DOES NOT REPLICATE AGAIN HERE!
  15. 15. Meiosis II  The daughter cells from Meiosis I divide again WITHOUT replicating their chromosomes  That leads to 4 gametes, each with half the number of chromosomes (haploid) as the original “mother” cell
  16. 16. Prophase II  Spindle fibers form and move chromosomes to center Metaphase II  Spindle fibers attach to the chromosomes  chromosomes line up in the middle of the cell – similar to how they do in Mitosis Anaphase II • Fibers pull the sister chromatids toward opposite ends of the cell Telophase II and Cytokinesis • Nuclear membranes form • Both cells separate – forming 4 new haploid cells
  17. 17. Oogenesis – meiosis in human female reproductive cells – makes eggs (ovum) • Total of 4 cells produced: • Forms one usable egg cell with a large supply of stored nutrients. • The other 3 cells, called polar bodies, disintegrate.
  18. 18. Spermatogenesis – meiosis in human male reproductive cells to make sperm (spermatazoa) • Produces 4 viable gametes • All 4 gametes produce a long whip-like tail
  19. 19. Meiosis:  Cell division necessary for sexual reproduction  Produces 4 daughter cells  Daughter cells are Haploid  Daughter cells are gametes (sexual repro. cells)  2 nuclear/cellular divisions  Vital to maintain correct number of offspring in sexually reproducing organisms  Crossing over = opportunity for genetic variability
  20. 20. Differentiate Mitosis Meiosis  Asexual reproduction  Used for sexual reproduction  Produces 2 daughter cells  Produces 4 daughter cells  Daughter cells are diploid  Daughter cells are Haploid  Daughter cells are  Daughter cells are genetically identical to each other and to parent cell  Produces somatic cells  One cell/nuclear division different from each other, and from parent cell  Produces gametes  Two nuclear/cellular divisions
  21. 21. Human chromosomal diseases **Mistake in meiosis can lead to an incorrect chromosomal number, causing consequences for offspring**  Down’s syndrome (extra chromosome #21)  Turner’s syndrome (missing or incomplete X chromosome in girls)  Klinefelter’s syndrome (males that have an extra X chromosome [XXY])
  22. 22. Think – Pair – Share  How does a baby with Down’s Syndrome end up with 3 chromosome #21s?
  23. 23. Video  Meiosis square dance

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