Cell Division and Mitosis

  1. Dividing Cells: The Bridge Between Generations

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    1. Overview of Division Mechanisms
      1. Mitosis and meiosis are eukaryotic nuclear division mechanisms that lead to the distribution of DNA to new nuclei in forthcoming daughter cells.
        1. Mitosis is used by multicelled organisms for development, growth, and repair.
        2. Meiosis occurs only in germ cells.
    2. Some Key Points About Chromosomes
      1. Each chromosomes is a molecule of DNA with proteins.

 

  1. The Cell Cycle
    1. The cell cycle is a cells life.
    2. Most of a cell’s existence (about 90 percent) is spent in interphase; mitosis occupies only a small part.
      1. During interphase the cell’s mass increases
      2. Some cells are arrested in interphase and never divide again (example: brain cells).

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  1. Stages of Mitosis—An Overview
    1. The four sequential stages of mitosis are: 

 

prophase

metaphase

anaphase

telophase

 

 

Meiosis

  1. Comparison of Asexual and Sexual Reproduction
    1. In asexual reproduction, one parent passes a duplicate of its genetic information to its offspring, which can only be genetically identical clones of the parent.
    2. In sexual reproduction, each parent contributes [one gene] for each trait.
    3. Two Divisions, Not One
      1. In some ways meiosis resembles mitosis:

     

     

  2. From Gametes to Offspring
    1. Gamete Formation in Animals

      1. The life cycle of multicelled animals proceeds from meiosis to gamete formation Þ fertilization Þ growth by mitosis.
      2. In males, meiosis and gamete formation is called spermatogenesis.
      3. In females, meiosis and gamete formation is called oogenesis.
    2. More Gene Shufflings at Fertilization
      1. The diploid chromosome number is restored at fertilization when two very different gamete nuclei fuse to form the zygote.
      2. The variation present at fertilization is from three sources:
        1. Crossing over occurs during prophase I.
        2. Random alignments at metaphase I lead to millions of combinations of maternal and paternal chromosomes in each gamete.
        3. Sexual selection: of all the genetically diverse gametes produced, chance will determine which two will meet.

  3. Meiosis and Mitosis Compared
    1. Both are eukaryotic processes.
    2. Mitotic cell division produces clones; this type of division is common in asexually reproducing organisms and in the growth process.
    3. Meiosis occurs only in the germ cells used in sexual reproduction; it gives rise to novel combinations