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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
    View slide
  • Meiosis
    • A cell replicates its DNA, then divides twice, forming four haploid cells
    • Stages are the same, but they occur TWICE!
    View slide
  • 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