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Meiosis

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Meiosis

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  1. Meiosis

  2. Why Do cells Go through Meiosis? • Cells go through Meiosis in order to make Sex Cells • Sex cells are also called Gametes • Four Daughter Cells are created • Haploid (1N)

  3. Interphase • Cell Grows • Duplicates DNA • Cell Prepares to divide

  4. After Interphase • In order to make sex cells or cells with half the number of chromosomes meiosis has TWO phases • Meiosis I and Meiosis II

  5. Prophase I • Chromosomes Condense (become visible) • Homologous chromosomes form a tetrad (4 chromatids)- paring up called SYNAPSIS • Crossing Over Occurs!

  6. Crossing Over • Homologous Chromosomes- Similar chromosomes and genes in the same location, but come from different parents • When the chromosomes touch they switch genetic information CROSSOVER • Causes genetic variation in the resulting gametes

  7. Knowledge Check • Why do cells go through meiosis? A- to replicate body cells B- To replicate sex cells • What’s the name of the type of cell formed through meiosis? A- gametes B- somatic cells • What important event leads to genetic variation? A- homologous chromosomes B- Tetrad C-Crossover

  8. Crossover close-up with results

  9. Metaphase I • Homologous chromosomes move together to the middle of the cell • Spindle attaches to the centromere

  10. Anaphase I • Homologous chromosomes separate • Sister chromatids stay attached • Move towards opposite poles

  11. Telophase I • Division of cytoplasm • Creates Two daughter cells • Begin Meiosis II • There is a brief interphase, but no DNA replication • Why?

  12. Knowledge Check • During Anaphase I in meiosis: A- The sister chromatids separate to opposite poles B- The homologous chromosomes separate to opposite poles Name the stage

  13. Prophase II • Spindles re-appear • Nuclear membrane stays separated

  14. Metaphase II • Chromosomes line up in the middle • Spindle attaches • How are metaphase I and II different?

  15. Anaphase II • Sister Chromatids Separate from each other • How are Anaphase I and II different from eachother?

  16. Telophase II • Nucleus reforms • Division into four daughter cells • Haploid (1N) • Gametes (egg and sperm)

  17. Knowledge Check- Name the phase

  18. Final Results of Meiosis • 4 haploid daughter cells which will develop into sex cells • Each daughter cell has half of the genetic information of a somatic cell • 23 chromosomes for each sex cell NOTE: Males will create 4 sperm cells for every one cell that goes through meiosis Females will create 4 egg cells, BUT 3 will turn into non usable polar bodies and 1 will mature into an egg cell.

  19. Let’s watch Meiosis in Motion • http://www.classzone.com/cz/books/bio_07/resources/htmls/animated_biology/unit3/bio_ch06_0175_ab_meiosis.html • http://www.sumanasinc.com/webcontent/animations/content/meiosis.html

  20. Through sexual reproduction and fertilization, these gametes fuse to form one diploid cell again (2n 46 chromosomes).

  21. Zygote= a fertilized egg • Zygote will begin to rapidly mitotically divide to make more cells to form a BLASTOCYST and then develop into an EMBRYO.

  22. Fertilization and Life • http://glencoe.mcgraw-hill.com/sites/dl/free/0078617022/161752/00053403.html

  23. Clay meiosis • As a class we will use the clay, yarn, and string to go through the phases of meiosis so that you can visually see what happens

  24. Create Prophase 1 with your clay and yarn- SHOW CROSSOVER

  25. Create metaphase 1 with your clay and yarn

  26. Create anaphase 1 with your clay and yarn

  27. Create Telophase 1 with your clay

  28. Move the chromosomes in position for prophase and metaphase 2- NOTICE EACH CHROMOSOME IS DIFFERENT

  29. Position the chromosomes, spindle fibers, and centrioles to anaphase II

  30. Position your chromosomes for telophase and cytokinesis

  31. Things to notice about the results • 4 resulting daughter cells. Contains only 1 set of genetic information in the chromosome haploidn • Each daughter cell contains chromosomes that are genetically different from one another • These daughter cells will develop into full sex cells (gametes). Sperm for males and egg for female