Student Lab Guide 1:
Mr. Dibble
Introduction and Instructions for Modeling Mitosis
Study mitosis in the cells of Mr. Dudley Dibble, an imaginary creature with four
chromosomes which are represented at different phases of mitosis by red and blue yarn
and large red and blue popsicle sticks. Work out each step of the process using bulletin
board paper for the cells and yarn for the cell membrane, nuclear membrane and
spindle fibers.
Go through the entire modeling process several times. Each group member takes a
turn as the “explainer”. Follow along with the steps below for the first one or two turns
and then follow them from memory. Answer the questions about each stage as you go
along and answer them each time you go through the process. Explain your answers in
your own words.
A. Introduction: Interphase and Chromosome Replication
1. Lay out on a table the bulletin board paper which represents a cell.
2. Tape the piece of black yarn to the paper in an oval shape to form the cell
membrane.
3. Tape the piece of purple yarn to the paper to form the nuclear membrane.
Throughout Interphase the chromosomes are extended and are NOT visible in the light
microscope. (Figure 1) The DNA is uncoiled and uncondensed. These will be
simulated with two pieces of red and two pieces of blue yarn.
4. Place two 12 inch pieces of red yarn and two 12 inch pieces of blue yarn inside the
nucleus of the cell. These pieces of yarn should be intertwined at this phase.
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FIGURE 1: Dibble Uncondensed Chromosomes
Uncoiled, uncondensed chromosomes
Cell Membrane
Nuclear Membrane
5. Prior to mitosis the chromosomes begin to coil up and condense which makes them
shorter and thicker and become visible. To represent this, cut the red yarn and the blue
yarn into 6 inch pieces. Place two pieces of the red yarn and two pieces of the blue
yarn back into the nucleus. This represents a diploid cell with two pairs of
chromosomes (Figure 2). At this point the chromosomes have NOT replicated.
FIGURE 2: Dibble Diploid Chromosome Set
Chromosomes
Cell Membrane
Nuclear Membrane
Answer the following questions:
1. What does diploid mean?
2. Are most human cells diploid?
3. Define homologous chromosomes.
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4. How many pairs of homologous chromosomes are present in the picture of the
Dibble cell above?
5. Draw a circle around each homologous pair of chromosomes in Fig. 2.
6. Are the homologues (a short name for homologous chromosomes) above paired with
one another in the cell or are they independent from one another?
7. What is the best description of homologues: a. they are the same size and shape; b.
they contain the same types of genes in the same order; c. they generally contain
different versions (alleles) of many of their genes; d. all of the above.
8. Contrast gene and allele.
During Interphase the DNA molecules replicate. This creates an exact copy
of each chromosome.
FIGURE 3: CHROMATID
Original chromosome
Replicated chromosome
Centromere
FIGURE 4: INTERPHASE CHROMOSOMES REPLICATED
Cell Membrane
Chromosomes
Nuclear Membrane
The nucleus initially contained four unreplicated chromosomes (two pieces of red yarn
and two pieces of blue yarn). During Interphase each chromosome makes an identical
copy of itself. The two identical chromosomes (sister chromatids) are attached at the
point called the centromere. (Figure 3) Represent the chromosome replication by
placing the two additional 6 inch pieces of the red yarn and the two additional 6 inch
pieces of the blue yarn in the nucleus. Use tape (representing the centromere) to attach
the sister chromatids. Now it contains four replicated chromosomes (four red pieces of
yarn and four blue pieces of yarn). (Figure 4)
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Answer the following questions:
1. A chromatid is made of DNA and which of the following: a. protein; b. carbohydrate;
c. lipid.
2. How do the sister chromatids differ from the chromosomes?
3. What is a centromere?
4. Contrast condensed (coiled) and extended (uncoiled) chromosomes.
B: PROPHASE: First Stage of Mitosis
1. Replace the red and blue yarn with two pair of red popsicle sticks held together by
rubber bands and two pair of blue popsicle sticks held together by rubber bands. This
represents replicated chromosomes condensed and visible held together at the
centromere (the rubber band represents the centromere).
2. In this phase the nuclear membrane disappears which allows the rest of the mitotic
events to occur. Remove the purple yarn that represents the nuclear membrane (put
aside for use later).
3. At each of the opposite sides of the cell, tape a green rectangular structure which
represents the two centrioles which are at right angles to each other.
4. Attach six pieces of the rust yarn (representing the spindle fibers) with tape across
the cell from one centriole to the other. Some of the spindle fibers attach to the
replicated chromosomes at their centromeres. Place each of the four pairs of replicated
chromosomes on a separate spindle fiber (Figure 5).
FIGURE 5: PROPHASE
Centrioles
Cell Membrane
Spindle Fibers
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Answer the following questions:
1. Are the two sister chromatids that are connected by a centromere identical to one
another or do they contain different alleles? Explain.
2. As noted above, these structures are called replicated chromosomes. Replicated
chromosomes are quite different from the unreplicated chromosomes seen earlier.
Compare replicated chromosomes to unreplicated ones by filling in the blanks below:
The amount of DNA in a replicated chromosome is ________ times the amount of DNA
in an unreplicated chromosome.
The number of copies of each gene in a replicated chromosome is _______ times the
number of copies in an unreplicated chromosome.
Each replicated chromosome contains _________ (number) of complete copies of
genetic information.
The copies of genetic information in each chromosome are: a. identical; b.
homologous; c. complementary.
3. Do you think that the homologous replicated chromosomes (the two pairs of blue/red
popsicle sticks) will pair with one another during mitosis? Explain.
4. How many sister chromatids are in your Dibble nucleus during Prophase?
5. A diploid human cell contains 46 unreplicated chromosomes in early Interphase.
How many sister chromatids will be present in the human cell during Prophase of
mitosis?
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C. METAPHASE: Second Stage of Mitosis
Figure 6: Metaphase
Metaphase plane
Centrioles
Spindle Fiber
1. Arrange your Dibble chromosomes (pairs of red and blue popsicle sticks) across the
center of the cell. (Figure 6)
Figure 7: Orientation of chromosomes
The specific order of chromosomes and their orientation (right side up, upside down) is
completely random.(Figure 7) In metaphase, replicated chromosomes are lined up on
the metaphase plane (across the center of the cell) by the spindle fibers. (Figure 6)
Homologous chromosomes are independent of one another. Homologous replicated
chromosomes, such as the two sets of red or blue popsicle sticks, are NOT PAIRED.
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Answer the following questions:
1. How many replicated chromosomes are on the metaphase plane in Dibble?
2. How many replicated chromosomes would be on the metaphase plane in a human
cell undergoing mitosis?
D. ANAPHASE: Third Stage of Mitosis
1. Remove the rubber bands and separate the popsicle sticks (sister chromatids) to
form daughter chromosomes. (Figure 8)
2. Cut the spindle fibers in half.
3. Daughter chromosomes are moved toward opposite poles by the spindle fibers in
Anaphase. They are pulled through the cytoplasm at the centromere.
Figure 8: Anaphase
Chromosomes
Cell Membrane
Centriole
Centriole
Spindle Fiber
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Answer the following questions:
1. Are the daughter chromosomes replicated or unreplicated?
2. Are the two sets of daughter chromosomes, the one moving toward the left and the
other toward the right, identical or non-identical?
3. Are the two sets of daughter chromosomes identical to those in the parent cell?
4. What is accomplished by this process?
E. TELEPHASE: The Last Stage of Mitosis
1. The spindle fibers disappear. Remove the rust yarn (spindle fibers) from your cell.
2. Daughter chromosomes (red and blue popsicle sticks) reach the poles (opposite
sides) of the cell. The daughter chromosomes start to uncoil and become extended.
Replace red and blue popsicle sticks with 6 inch pieces of red and blue yarn (uncoiled
chromosomes).
3. Two new nuclear membranes form; one around each set of daughter chromosomes
(red and blue yarn). Cut the purple yarn in half to create the two new nuclear
membranes in your cell. (Figure 9)
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4. In animal cells the cell membrane (black yarn) will begin to pinch in, starting a
division in the cytoplasm. (Figure 9)
Figure 9: Telophase
Cell Membrane
Nuclear Membrane
Chromosomes
Cleavage Furrow
F. Cytokinesis: Cell Division; Two Daughter Cells Formed
1. The cytoplasm of an animal cell pinches in half at the center (Figure 9) from the
outside in, until it has produced two separate daughter cells (Figure 10). Divide your
cell in half in this manner by replacing the long black yarn. Cut the black yarn which
represented the parent cell membrane into two equal pieces. These two shorter pieces
of black yarn represent the membranes of the two NEW daughter cells. Use the
purple yarn from the previous cells to make the two new nuclear membranes. (Figure
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Figure 10: Cytokinesis Completed; Two Daughter Cells
Cell Membrane
Nuclear Membrane
Chromosomes
Cell Membrane
Chromosomes
Nuclear Membrane
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2. The daughter cells are now entering the early Interphase Stage. Your Dibble
chromosomes are continuing to uncoil and become less condensed. Replace the two
red and blue 6 inch pieces of yarn with two red and blue 12 inch pieces of yarn.
Intertwine the red and blue pieces. This represents the daughter cells entering a new
Cell Cycle. The cells will grow to full size and, if continuing to divide, will replicate the
Dibble chromosomes and will repeat the cycle again. (Figure 11)
Figure 11: Early Interphase
Nuclear Membrane
Cell Membrane
Chromosomes
Answer the following questions:
1. Does the parent cell still exist?
2. How are these daughter cells related to one another?
3. How are these daughter cells related to the parent cell?
4. Overall, what has been accomplished by mitosis?
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5. You have used your materials to model mitosis (nuclear division) and cellular
division. Explain some ways in which a model (like you used) differs from the actual
things and processes it represents.
PRACTICE
As you noted above, you should go through the entire process several times with each
group member taking a turn as the “explainer”. Follow along with the procedures in the
Student Lab Handout for the first one or two turns, and then go through two or more
repetitions from memory. You may also refer to Table 1 below for a rough guide. Your
teammates can assist you by asking questions and giving hints.
TABLE 1
Interphase
G1 Stage:
Growth & development of
the cell
Protein synthesis
S-phase:
Chromosomes replicate
(DNA makes an exact copy
of itself)
G 2 Stage:
Growth and development
Organelle replication
Mitosis
Prophase:
Replicated chromosomes
condense
Nuclear membrane
dissolves
Spindle fibers form
Metaphase:
Replicated chromosomes
line up across the center of
the cell
Anaphase:
Sister chromatids separate
Daughter chromosomes
move to opposite poles
Telophase:
Cytoplasm begins to
separate
New nuclear membranes
form
Spindle fibers disappear
Cytokinesis
Complete cell division
occurs
Produces two daughter
cells
Prepared by: Dr. Debbie Payne, Ruth H. Liddell, Shirley K. Scarbrough
Alabama State University, Math, Science Partnership, Winter,2013
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