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Biology - Meiosis

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    Biology - Meiosis Biology - Meiosis Presentation Transcript

    • Meiosis Textbook Sections 11.1 and 11.2
    • Sexual Reproduction
      • Organisms receive half of their DNA from each parent
      • Sperm and eggs cells (haploid) combine to create a zygote (diploid)
      • Used by most animals, fungi, plants, and algae
    • Remember…
      • Organisms have two copies of each chromosome, called “homologous chromosomes”
      • Can be autosomes or sex chromosomes
    • Meiosis
      • A cell replicates its DNA, then divides twice, forming four haploid cells
      • Stages are the same, but they occur TWICE!
    • Meiosis I vs. Meiosis II
    • Steps of Meiosis
      • PROPHASE I
    • Steps of Meiosis
      • METAPHASE I
        • Homologous chromosomes line up along center
    • Steps of Meiosis
      • ANAPHASE I
        • Sister chromatids DO NOT separate.
        • Homologous chromosomes DO!
      • TELEPHASE I
    • Steps of Meiosis
      • PROPHASE II
        • Cell has been split in two
        • No nuclear membrane forms
    • Steps of Meiosis
      • Occurs in both cells
      • METAPHASE II
    • Steps of Meiosis
      • ANAPHASE II
      • TELEPHASE II
    • THE OFT-FORGOTTEN DIFFERENCE
      • In the first cell division, CHROMOSOME PAIRS are separated.
      • In the second cell division, SISTER CHROMATIDS are pulled apart.
    • Comparing Mitosis and Meiosis
      • Mitosis makes cells for growth, development, repair, and asexual reproduction
      • Meiosis makes cells for sexual reproduction
    • Comparing Mitosis and Meiosis
      • Mitosis produces two cells identical to the parent cell (called daughter cells)
      • Meiosis produces four cells with half the number of chromosomes as the parent
    • Comparing Mitosis and Meiosis
      • In meiosis , “crossing over” occurs during metaphase I.
      • Chromosomes form tetrads
      • Homologous chromosomes “swap” parts of their DNA  leads to genetic variation
    • Sperm vs. Eggs
      • Spermatogenesis creates four equally-sized sperm cells
      • Oogenesis creates three tiny cells that will die (polar bodies) and one large ovum (egg)
    • Spermatogenesis vs. Oogenesis