Chapter 17 | Cell Reproduction and Meiosis

  1. Figure 17.7 Which of the following is the correct order of events in mitosis?
    1. Sister chromatids line up at the metaphase plate. The kinetochore becomes attached to the mitotic spindle. The nucleus reforms and the cell divides. Cohesin proteins break down and the sister chromatids separate.
    2. The kinetochore becomes attached to the mitotic spindle. Cohesin proteins break down and the sister chromatids separate. Sister chromatids line up at the metaphase plate. The nucleus reforms and the cell divides.
    3. The kinetochore becomes attached to the cohesin proteins. Sister chromatids line up at the metaphase plate. The kinetochore breaks down and the sister chromatids separate. The nucleus reforms and the cell divides.
    4. The kinetochore becomes attached to the mitotic spindle. Sister chromatids line up at the metaphase plate. Cohesin proteins break down and the sister chromatids separate. The nucleus reforms and the cell divides.
      This diagram shows the five phases of mitosis and cytokinesis. During prophase, the chromosomes condense and become visible, spindle fibers emerge from the centrosomes, the nuclear envelope breaks down, and the nucleolus disappears. During prometaphase, the chromosomes continue to condense and kinetochores appear at the centromeres. Mitotic spindle microtubules attach to the kinetochores, and centrosomes move toward opposite poles. During metaphase, the mitotic spindle is fully developed, and centrosomes are at opposite poles of the cell. Chromosomes line up at the metaphase plate and each sister chromatid is attached to a spindle fiber originating from the opposite pole. During anaphase, the cohesin proteins that were binding the sister chromatids together break down. The sister chromatids, which are now called chromosomes, move toward opposite poles of the cell. Non-kinetochore spindle fibers lengthen, elongating the cell. During telophase, chromosomes arrive at the opposite poles and begin to decondense. The nuclear envelope reforms. During cytokinesis in animals, a cleavage furrow separates the two daughter cells. In plants, a cell plate separates the two cells.
      Figure 17.7 Karyokinesis (or mitosis) is divided into five stages—prophase, prometaphase, metaphase, anaphase, and telophase. The pictures at the bottom were taken by fluorescence microscopy (hence, the black background) of cells artificially stained by fluorescent dyes: blue fluorescence indicates DNA (chromosomes) and green fluorescence indicates microtubules (spindle apparatus). (credit “mitosis drawings”: modification of work by Mariana Ruiz Villareal; credit “micrographs”: modification of work by Roy van Heesbeen; credit “cytokinesis micrograph”: Wadsworth Center/New York State Department of Health; scale-bar data from Matt Russell)
  2. Figure 17.14 Rb and other proteins that negatively regulate the cell cycle are sometimes called tumor suppressors. Why do you think the name tumor suppressor might be an appropriate for these proteins?
    This illustration shows the regulation of the cell cycle by the upper case R lower case b protein. Unphosphorylated upper R lower b binds the transcription factor E 2 F. E 2 F cannot bind the D N A, and transcription is blocked. Cell growth triggers the phosphorylation of R b. Phosphorylated R b releases E 2 F, which binds the D N A and turns on gene expression, thus advancing the cell cycle.
    Figure 17.14 Rb halts the cell cycle and releases its hold in response to cell growth.
  3. Figure 17.22 If a mutation occurs so that a fungus is no longer able to produce a minus mating type, will it still be able to reproduce?
    This illustration shows the life cycle of fungi. In fungi, the diploid (2n) zygospore undergoes meiosis to form haploid (1n) spores. Mitosis of the spores occurs to form hyphae. Hyphae can undergo asexual reproduction to form more spores, or they form plus and minus mating types that undergo nuclear fusion to form a zygospore.
    Figure 17.22 Fungi, such as black bread mold (Rhizopus nigricans), have haploid-dominant life cycles. The haploid multicellular stage produces specialized haploid cells by mitosis that fuse to form a diploid zygote. The zygote undergoes meiosis to produce haploid spores. Each spore gives rise to a multicellular haploid organism by mitosis. (credit “zygomycota” micrograph: modification of work by “Fanaberka”/Wikimedia Commons)

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