Cell Cycle – Cells go through the cell cycle to increase the number of cells for the purpose of growth and development, repair of injury, replacement of worn out cells, and asexual reproduction.

Interphase

    G₁ – (Gap 1) - increase in size

    S – (Synthesis) – DNA replication (chromosome doubling) occurs

    G₂ – (Gap 2) – organelles are doubled

    Cell Division

        Mitosis – division of the nucleus

            Prophase – nuclear membrane comes apart, chromosomes shorten

           Metaphase – chromosomes line up at the middle (equatorial plane)

           Anaphase – doubled chromosomes (sister chromatids) separate

           Telophase – nuclear membranes form and chromosomes lengthen

            Cytokinesis – division of the cytoplasm

                In plants cells – cell plate formation (cell wall prevents pinching off)

                In animal cells – cleavage furrow formation – pinching off.

Cancer – Cells that lose their ability to stop dividing.

• Either have too much GO protein or not enough STOP protein.
• Resulting from DNA mutation that is inherited or occurs during ones lifetime possibly due to a virus, chemical,                                            or ultraviolet radiation.  Could also be the result of a random mutation during DNA replication.
• Results in masses of cells called tumors.

    Two kinds of tumors:

        Benign – self-contained mass of cells

        Malignant – mass of cells capable of metastasis (spreading)

Meiosis: Another kind of cell division.

    Purpose – production of gametes for sexual reproduction.

        Oogenesis – the production of egg cells (ova).  One cell splits unevenly into 1 egg and 3 polar bodies.

        Spermatogenesis – the production of sperm cells.  One cell splits into 4 sperm cells

    Consists of two divisions following an interphase:

        Interphase – Chromosomes doubled

        Meiosis I

            Prophase I – homologous chromosomes pair up (synapsis) = tetrads

            Metaphase I - tetrads (homologous chromosome pairs) line up in middle

            Anaphase I – homologous chromosomes separate

            Telophase I and cytokinesis – 2 cells are formed, each goes to meiosis II

       Meiosis II

            Prophase II -

            Metaphase II – chromosomes line up in middle

            Anaphase II – sister chromatids separate

            Telophase II and cytokinesis – 4 haploid (n) cells are formed