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Meiosis

Meiosis. Formation of Sex Cells. Meiosis. A process of reduction division in which the number of chromosomes per cell is cut in half through the separation of homologous chromosomes in a diploid cell. Diploid – 2 sets of chromosomes Haploid – 1 set of chromosomes

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Meiosis

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  1. Meiosis Formation of Sex Cells

  2. Meiosis • A process of reduction division in which the number of chromosomes per cell is cut in half through the separation of homologous chromosomes in a diploid cell. • Diploid – 2 sets of chromosomes • Haploid – 1 set of chromosomes • Homologous – chromosomes that each have a corresponding chromosome from the opposite sex parent

  3. Meiosis

  4. Meiosis Stages • Meiosis usually involves 2 distinct stages • Meiosis I • Meiosis II

  5. Prophase I • Each chromosome pairs with its corresponding homologous chromosome to form a tetrad. • Each tetrad is made of 2 chromosomes, each with a copy attached forming sister chromatids • The pairing of homologous chromosomes is the key to understanding meiosis. • Crossing-over may occur here • Crossing-over is when chromosomes overlap and exchange portions of their chromatids.

  6. Prophase I http://videos.howstuffworks.com/hsw/5987-mitosis-and-meiosis-prophase-one-video.htm

  7. Metaphase I • Spindle fibers attach to the chromosomes

  8. Metaphase I http://videos.howstuffworks.com/hsw/5988-mitosis-and-meiosis-metaphase-one-video.htm

  9. Anaphase I • The fibers pull the homologous chromosomes toward opposite ends of the cell. • Notice that in anaphase I the sister chromatids remain attached at their centromeres and move together toward the poles. • A key difference between mitosis and meiosis is that sister chromatids remain joined after metaphase in meiosis I, whereas in mitosis they separate.

  10. Anaphase I http://videos.howstuffworks.com/hsw/5989-mitosis-and-meiosis-anaphase-one-video.htm

  11. Telophase I • A nuclear envelope reforms around each chromosome set, the spindle disappers, and cytokinesis follows.

  12. Telophase 1 http://videos.howstuffworks.com/hsw/5990-mitosis-and-meiosis-telophase-one-video.htm

  13. Cytokinesis • Cytokinesis is not one of the stages or phases of meiosis or mitosis. It is the process of division that the cytoplasm undergoes when it is distributed into daughter cells • In animal cells, cytokinesis involves the formation of a cleavage furrow, resulting in the pinching of the cell into two cells. • After cytokinesis, each of the two progeny cells has a nucleus with a haploid set of replicated chromosomes.

  14. Cytokinesis

  15. Prophase II • Meiosis I results in two haploid (N) cells. • Each cell has half the number of chromosomes as the original cell. • There is no DNA replication between the two cell divisions. • The nuclear envelope breaks down, and the spindle apparatus forms.

  16. Prophase II http://videos.howstuffworks.com/hsw/5991-mitosis-and-meiosis-prophase-two-video.htm

  17. Metaphase II • The chromosomes line up similar to metaphase in mitosis.

  18. Metaphase II http://videos.howstuffworks.com/hsw/5992-mitosis-and-meiosis-metaphase-two-video.htm

  19. Anaphase II • Sister chromatids separate and move to opposite ends of the cell.

  20. Anaphase II http://videos.howstuffworks.com/hsw/5993-mitosis-and-meiosis-anaphase-two-video.htm

  21. Telophase II • Meiosis II results in 4 haploid cells (gametes in animals) • Because of crossing-over, some chromosomes are seen to have recombined segments of the original parental chromosomes.

  22. Telophase II http://videos.howstuffworks.com/hsw/5994-mitosis-and-meiosis-telophase-two-video.htm

  23. Gamete Formation • In males, meiosis results in 4 sperm cells • In females, meiosis results in 1 egg cell and three polar bodies, which are not used in reproduction.

  24. Stages of Meiosis http://highered.mcgraw-hill.com/olcweb/cgi/pluginpop.cgi?it=swf::535::535::/sites/dl/free/0072437316/120074/bio19.swf::Stages%20of%20Meiosis

  25. Mitosis vs Meiosis

  26. How Cells Divide: Mitosis vs Meiosis http://www.teachersdomain.org/resource/tdc02.sci.life.gen.mitosis/

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