Worksheet for Morgan/Carter Laboratory #7 Mitosis and Meiosis Ex. 7-1: MODELING THE CELL CYCLE AND MITOSIS IN AN ANIMAL CELL Lab Study A: Interphase How many pairs of homologous chromosomes are present in the cell during this stage of the cell cycle? Lab Study B: M Phase (Mitosis and Cytokinesis) What structures make up the fibers of the spindle? Referring to your model, how many duplicated chromosomes are present in the prometaphase nucleus? Draw and label Figure 7.6 with chromosome, spindle fibers, centrosome, centrioles, kinetochore, equator. Describe the movement of the chromosome arms as you move the centromeres to the poles (1 sentence). Summarize the current hypothesis for chromosome movement toward the poles referred to in your lab text. How many chromosomes are in each new nucleus? How many were present when this exercise began? How would the condition of telomeres have changed from a previous cell cycle (see lab text)?
Ex. 7-2: OBSERVING MITOSIS AND CYTOKINESIS IN PLANT CELLS Interphase (G 1, S, G 2) Prophase Prometaphase Metaphase Anaphase Telophase Ex. 7-3: OBSERVING CHROMOSOMES, MITOSIS AND CYTOKINESIS IN ANIMAL CELLS Lab Study A: Mitosis in Whitefish Blastula Cells Prophase Metaphase
Anaphase Telophase/Cytokinesis List 3 major differences you have observed between mitosis in animal cells and mitosis in plant cells. Lab Study B: Human Chromosomes in Dividing Leukocytes Count the chromosomes in one cell in the field of view. Are the chromosomes from a person with a normal chromosome number? Ex. 7-4: MODELING MEIOSIS What would be the consequences in successive generations of offspring if the chromosome number were not reduced during meiosis? Lab Study A: Interphase In G 1, are the chromosomes single or duplicated? What color should the sister chromosomes be for each pair? Lab Study B: Meiosis I How many tetrad complexes do you have in your cell, which is 2n = 4? What combinations of alleles are now present on the chromatids? How does the structure of chromosomes in anaphase I differ from that in anaphase of mitosis? Two nuclei now form, followed by cytokinesis. How many chromosomes are in each nucleus? Would you describe the new nuclei as being diploid (2n) or haploid (1n)?
How has crossing over changed the combination of alleles in the new nuclei? Are both chromosomes of the same color in the same nucleus? (compare your results with others) Lab Study C: Meiosis II What is the total number of nuclei and cells now present? How many chromosomes are in each? How many cells were present when the entire process began (before Meiosis I)? How many chromosomes were present when the entire process began? How many of the cells formed by the meiotic division just modeled are genetically identical? Explain your results in terms of independent assortment and crossing over. Summarize the major differences between mitosis and meiosis in the table below: Synapsis Crossing over When chromosomes split Chromosome structure and movement during anaphase Number of divisions Number of cells resulting Number of chromosomes in daughter cells Genetic similarity of daughter c ells to parent cells Mitosis Meiosis
Reviewing Your Knowledge 1. Define the following terms: mitosis: meiosis: cytokinesis: chromatin: centromere: centriole: centrosome: kinetochore: spindle: aster: sister chromatid: nucleolus: cell plate: cleavage furrow: diploid: haploid: 2. In the photomicrograph of dividing root cells below, identify interphase and the following phases of mitosis: prophase, metaphase, anaphase, telophase, and cytokinesis.
3. Answer the following questions based on the drawings of the phases of meiosis on page 173: a. Using the designated letters, list the phases of meiosis in sequence. b. Label each stage (include I or II). A B C D E F c. At what stage would crossing over occur? d. What is the diploid number for this organism? 4. Mitosis is important as organisms, both animals and plants, increase in size and grow new tissues and organs. Unlike animals, plants continue to grow throughout their lives. Where would you expect mitosis to be most common in the body of a mature plant? 5. What role would mitosis play in the body of an adult animal? 6. What advantage does the process of crossing over bring to reproduction? 7. Why would the method of cytokinesis in animal cells not work in plant cells?