Pre-Lab #4 Cell Division

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Pre-Lab #4 Cell Division Powered By Docstoc
					Pre-Lab #4: Cell Division                       Name _______________________________

1. Using your own words define the following:

       a. Mitosis

       b. Meiosis

       c. Chromosome

       d. Chromatid

       e. Centromere

       f. Homologous Pair

2. What is the purpose of mitosis?

3. What is the purpose of meiosis?

                                     Lab #4: Cell Division
Work in groups of two. Bring your textbook to lab.

   Cell theory says that all organisms are made of cells, and all cells come from preexisting cells. This
   means that cells must have some way of reproducing themselves. They have two ways:

   Mitosis: cell division producing daughter cells with the same chromosome number as the parent cell.
   Meiosis: cell division producing daughter cells with half the chromosome number of the parent cell.


 1. Identify the phases of mitosis using pop-beads and observing plant cells.
 2. Place the phases of mitosis and meiosis in proper sequence.
 3. Explain the consequences of both mitosis and meiosis.


A: Pop-Bead Activity

   Pop-beads are small, colored beads that can be joined together to simulate chromosome strands. We
   will use the pop-it beads to simulate the process that chromosomes undergo during cell division. We
   start with a cell with a chromosome number of 4 (4 chromosomes, or 2 homologous pairs). A
   homologous pair of chromosomes are two chromosomes of the same shape and size, one from the
   male parent and the other from the female parent. We will use red to identify the chromosome from
   the male parent and yellow for the chromosome from the female parent.

    1. Make 4 chromosomes: two long chromosomes (one red and one yellow) and two short
       chromosomes (one red, one yellow). The two long chromosomes should each have the same
       number of beads, as should the two short chromosomes. The two long chromosomes are one
       homologous pair; the two short chromosomes are the second homologous pair.

    2. Replicate your chromosomes by making an identical set of pop-it bead chromosomes (you should
       have a total of eight pop-it bead strands; four long and four short). Attach the identical replicas
       (chromatids) by their magnetic centromeres (remember a centromere is the region of the
       chromosome where duplicated strands of a chromosome are attached). You are now ready to
       proceed with mitosis.

    3. Move the “chromosomes” through each of the four stages of mitosis. Draw and label the pop-
       bead chromosomes for ONE of the phases on a separate sheet. (It is not necessary to draw each
       individual bead.)

B: Microscope Activity
Most of the cells you will see on prepared slides of mitotic tissues will be in interphase, since this is the
longest phase of the cell cycle. In this phase, DNA is being used to make protein and the DNA itself is
replicated, so the chromosomes are loose and unwound and impossible to see even using a microscope.
The chromosomes are not visible until the cells enter prophase, the first phase of mitosis. It will be
possible to see condensed chromosomes in all four phases of mitosis. Keep in mind that the process of
mitosis is continuous and the separations of the various stages are arbitrary. Many of the mitotic cells
you see may be in some intermediate point between the phases you have learned about.

1. Mitosis in Plant Cells: Prepared Slide of Onion Root Tip

 The tip of a plant root is the growing portion of the root and contains many cells undergoing mitosis.
    For each drawing, write your name and date and draw the cell large (~ 1/2 sheet of paper)

   1. After using the low power lens to focus your microscope, use the 40X objective lens to scan the
       specimen. You may choose to use the 100X oil immersion lens to observe the cells in detail.

   2. Draw and label one cell in interphase. Remember the proper techniques for drawing microscope
       specimens you learned in Lab #1!

   3. Draw and label two cells, one each in any two phases of mitosis. Identify the mitotic stage and
       label the identifiable features of the cell.

   4. Be sure to clean the oil off the slide with soap and water before you put away the microscope.


A: Reviewing Meiosis

1. Pop-Bead Activity

    Using your book as a guide and the 4 pop-bead chromosomes you created earlier, simulate each of
    the phases of meiosis in division I and division II. You should come away with a general idea of the
    process of meiosis I and meiosis II, and how these stages compare to mitosis.

     1. Draw the chromosomes as they would appear during metaphase I of meiosis.
     2. Draw the chromosomes as they would appear at the conclusion of telophase I.
     3. Draw the chromosomes as they would appear at the end of telophase II.

2. Chromosomes or Chromatids?

    The parasitic worm Ascaris has four chromosomes in each of its diploid (2N) cells. How many
    chromosomes are present in a cell at the end of each of the following stages? How many
    chromatids? (Remember: a chromosome is defined by its centromere. Whatever is attached to one
    centromere is considered one chromosome. When duplicated, identical strands of the chromosome
    are attached to one centromere, each strand is called a chromatid.)

             Stage of meiosis            # Chromosomes               # Chromatids
             Prophase I

             Prophase II

             Telophase II

Remember: a chromosome is defined by its centromere. Whatever is attached to one centromere
is considered one chromosome. When two identical DNA molecules are attached to one
centromere after replication, each is called a chromatid.

Lab Questions

 1. The life cycle of a cell consists of interphase and four phases of mitosis. In which part of the life
    cycle does a cell spend most time?

 2. What data or observations did you acquire during the lab to support your answer?

 3. Why can’t you see chromosomes in cells during interphase?

 4. Why can’t you see a nucleus in cells during cell division?

 5. Describe at least three major differences between metaphase in mitosis and metaphase I in meiosis?

 6. How does the number of human chromosomes before and after mitosis compare to the number of
    chromosomes before and after meiosis?

Simulating Mitosis and Meiosis: Illustrate how your pop-bead “chromosomes” are arranged in
each of the stages of mitosis and meiosis. Use different colors to distinguish the chromosome pairs. Note
the chromosome number at each stage. Include an example of crossing-over.

                           A COMPARISON OF MITOSIS AND MEIOSIS

                         MITOSIS                                                          2N = 4
                                     2N = 4
                                                  Prophase I


                                                  Metaphase I

                                                  Anaphase I

                                                  Telophase I

                                                    N=                                         N=

                                                                       Prophase II

                                                                      Metaphase II

      Telophase                                                        Anaphase II

                                                                      Telophase II

                  2N =             2N =            5
                                                    N=           N=                  N=            N=
                                          Mitosis               Meiosis
Number of cells at start of

Number of cells at end of

Number of cell divisions

Chromosome number in
terms of N                     Start   -------> End   Start   -------> End

Number of chromosomes in
the cell at start of process
(human cell)

Number of chromosomes in
the cell at end of process
(human cell)

Are the daughter cells
diploid or haploid?

Is the genetic make-up of
daughter cells unique or
identical to other cells in
the organism?

Role in the life cycle of an

Type of cells in a human
that can undergo this


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