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Meiosis

Meiosis. Box 55. Meiosis results in cells with ½ the # of chromosomes, so they can combine in sexual reproduction , which results in an embryo with the normal amount of chromosomes.

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Meiosis

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  1. Meiosis Box 55 Meiosis results in cells with ½ the # of chromosomes, so they can combine in sexual reproduction, which results in an embryo with the normal amount of chromosomes. • To solve this problem, the cells in the gametes (eggs and sperm), undergo Meiosis instead of Mitosis, when they divide. • Why Meiosis? • Most cells in our body are Diploid (“di” = 2) • Diploid = have 2 sets of chromosomes, 2n(one from mom, one from dad) • Sex cells, or gametes, are Haploid • Haploid = have 1 set of chromosomes, 1n Box 53 Box 41 Box 54 Box 42

  2. Chromosome Number Box 56 Homologous chromosomes= 2 sets of similar chromosomes, one from mom, one from dad • An example. • Fruit Flies (Drosophila), have 8 chromosomes total – 4 from dad fruit fly, 4 from mom fruit fly. Box 43 2n = 8 Diploid number? Haploid number? 1n = 4

  3. Phases of Meiosis Homologous = same chromosome, it just comes from different parents (mom or dad) • How are haploid (1n) gamete cells produced from diploid (2n) cells? • By Meiosis (my-OH-sis) • Meiosis = process of reduction cell division where the # of chromosomes per cell is cut in ½ by the separation of homologous chromosomes Box 57 Box 45 Box 58 Box 46 • Meiosis involves 2 distinct divisions, • Meiosis I • Meiosis II • Results of Meiosis? = cells with a haploid (1n) number of chromosomes Box 59

  4. Meiosis I Box 61 Prophase I = Each chromosome pairs up with its matching homologous chromosome forming a tetrad Interphase I = Cells undergo a round of DNA replication, forming duplicate chromosomes Tetrads= in prophase I, chromosomes duplicate and form a structure with 4 chromosomes (tetrad) Box 60 Box 62 4 sister chromatids form a Tetrad 2 sister chromatids Interphase I Prophase I Chromosome duplication

  5. During prophase I of Meiosis, when the tetrads form, a phenomenon called “Crossing Over” can occur. Crossing Over = results in the exchange of genetic information between homologous chromosomes Box 63 You got peanut butter in my chocolate! You got chocolate in my peanut butter! Sorry! Hey hot stuff, wanna dance? Owww! My arm! Who me? I think he likes me! Help!

  6. Meiosis I Anaphase I = Fibers pull the homologous chromosomes towards opposite ends of the cell (“A” for apart) Prophase I = Each chromosome pairs up with its corresponding homologous chromosome to form a tetrad Box 64 Metaphase I = Spindle fibers attach to the chromosomes, then they line up in the middle (“M” for middle) Interphase I = Cells undergo a round of DNA replication, forming duplicate chromosomes Box 65 Interphase I Prophase I Metaphase I Anaphase I

  7. Meiosis I Anaphase I = Fibers pull the homologous chromosomes towards opposite ends of the cell (“A” for apart) Prophase I = Each chromosome pairs up with its corresponding homologous chromosome to form a tetrad Metaphase I = Spindle fibers attach to the chromosomes, then they line up in the middle (“M” for middle) Telophase I and Cytokinesis = Nuclear membranes form, the cell separates into 2 new cells Interphase I = Cells undergo a round of DNA replication, forming duplicate chromosomes Box 66 Interphase I Prophase I Metaphase I Anaphase I Telophase and Cytokinesis

  8. Meiosis II Prophase II = of meiosis I results in 2 haploid daughter cells, each with ½ the # of chromosomes as the original cell Box 67 The 2 new cells now enter a 2nd round of meiotic division No more chromosome duplication prophase II

  9. Meiosis II Metaphase II = chromosomes line up in the middle Box 68 metaphase II prophase II Prophase II = of meiosis I results in 2 haploid daughter cells, each with ½ the # of chromosomes as the original cell

  10. Meiosis II Anaphase II = sister chromatids separate and move to opposite ends of the cell Box 69 Prophase II = of meiosis I results in 2 haploid daughter cells, each with ½ the # of chromosomes as the original cell Metaphase II = chromosomes line up in the middle Telophase II and Cytokinesis = of meiosis II results in 4 haploid (1n) daughter cells Box 70 4 3 metaphase II anaphase II telophase II prophase II 2 1

  11. Flow Chart for Meiosis I P Interphase I M Prophase I A Metaphase I Anaphase I T 92 Telophase I &Cytokinesis 92 92 92 Humans = 2n = 46 46 P Prophase II A M T Telophase II & Cytokinesis Anaphase II Metaphase II 46 23 46 46 4 daughter cells with haploid # (1n) I then …PMAT…..PMAT

  12. Gamete Formation For Sexual Reproduction, where egg and sperm unite to make an embryo Box 72 • Why do we even have Meiosis? • To make gametes (eggs and sperm). • Male gametes = sperm • Female gametes = eggs Box 71 Skip Box 59 Why do we need eggs and sperm? End of Chapter 10 and Chapter 11 Section 11-4

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