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Chapter 7 Meiosis

Chapter 7 Meiosis. Meiosis. Forms haploid gamete or spore cells Type of cell division that halves the number of chromosomes Creates 4 genetically different cells. Steps to Meiosis I.

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Chapter 7 Meiosis

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  1. Chapter 7 Meiosis

  2. Meiosis • Forms haploid gamete or spore cells • Type of cell division that halves the number of chromosomes • Creates 4 genetically different cells

  3. Steps to Meiosis I • Prophase I – Chromosomes condense, nuclear membrane breaks down, homologous chromosomes pair up and crossing-over occurs • Crossing-over – when homologous chromosome pairs exchange genetic material

  4. http://www.zerobio.com/crossing_over.htm

  5. Metaphase I • Pairs of homologous chromosomes line up together (like holding hands)

  6. Anaphase I • Pairs separate (NOT CHROMATIDS) and are pulled to opposite ends of the cell

  7. Telophase I • Chromosomes gather at the poles • Cytokinesis then occurs • DNA does not replicate to start Meiosis II

  8. Prophase II New spindle forms

  9. Metaphase II • Chromosomes line up along the middle of the cell (just like Mitosis)

  10. Anaphase II • Centromeres divide, chromatids separate, and move towards the poles of the cell

  11. Telophase II – Nuclear membrane forms around each set of chromosomes • Cytokinesis occurs

  12. http://highered.mcgraw-hill.com/sites/0072437316/student_view0/chapter12/animations.html#http://highered.mcgraw-hill.com/sites/0072437316/student_view0/chapter12/animations.html#

  13. http://www.johnkyrk.com/meiosis.html

  14. Genetic Diversity • Meiosis contributes to genetic diversity • Makes sure all organisms are genetically different

  15. Independent Assortment • The random distribution of homologous chromosomes during Meiosis

  16. Crossing-Over • DNA exchanged between homologous chromosomes during Prophase I

  17. Random Fertilization • Random sperm cell fuses with a random egg cell

  18. http://biog-101-104.bio.cornell.edu/BioG101_104/tutorials/cell_division/CDCK/cdck.htmlhttp://biog-101-104.bio.cornell.edu/BioG101_104/tutorials/cell_division/CDCK/cdck.html

  19. Oogenesis • Process that creates female egg cells • Of the four haploid cells created during Meiosis, three will die as polar bodies and one will survive as an egg cell

  20. Spermatogenesis • Process that creates male sperm cells • All four haploid gamete cells will develop into sperm cells

  21. 7-2 Sexual Reproduction • Asexual – One parent • Creates offspring that are clones • Sexual Reproduction – two parents • Creates genetically different offspring

  22. Advantages for Each • Asexual allows organisms to produce many offspring in a short amount of time • Sexual reproduction creates genetic diversity

  23. Disadvantages for Both • Asexual creates very little genetic diversity • Sexually reproducing organisms depend on finding mates (takes time and NRG)

  24. Alternation of Generations • Organisms cycle through diploid and haploid life stages • Haploid Life Cycle – haploid cells occupy the major portion of the life cycle (protists, fungi)

  25. Diploid Life Cycle - adult individuals are diploid, gametes are the only haploid cells (animals) • Alternation of Generations – plants, algae, and some protists alternate between a haploid and diploid phase • Sporophyte – diploid phase when spores are made

  26. Gametophyte - haploid phase where gametes are made

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