Modeling Crossing Over of Alleles and Resulting Daughter Cells
Interphase I
Use the supplies provided in the bag to create two homologous chromosomes.
1. Add eight pink beads to white pipe cleaner. The pipe cleaner represents one
chromatid and the beads represent genes inherited by the organism from the
mother.
2. Alphabatize and label the beads starting with the top bead as either “A” or “a” and
ending with the lowest bead as “H” or “h”. The letters written on each bead represent alleles of each
gene.
3. Add eight pink beads to the second white pipe cleaner.
4. Label the eight pink beads to create and exact match to the original white pipe cleaner. This second
pipe cleaner represents a duplicated copy of the DNA.
5. Twist the two white wires around one another between the fourth and fifth beads. The twisted pipe
cleaners represent one chromosome and the twist represents the centromere that binds the two sister
chromatids together.
6. Add eight blue beads to one blue pipe cleaner. The pipe cleaner and blue beads represent the
chromosome inherited from the father.
7. Mark the beads with the same sequence of letters as on the white pipe cleaners, but vary the
capitalization on some of the beads. (For example, if the first pink bead is “A” the first blue bead may
be “A” or “a”.)
8. Add eight blue beads to the second blue pipe cleaner.
9. Label the eight blue beads to create an exact match to the original blue pipe cleaner.
10. Twist the two blue pipe cleaners around one another between the fourth and fifth beads.
Color the diagram of the two wire chromosome structures in the figure below.
From mother
From father
QUESTION: How are the beads of the same color but on different wires related to one another.
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Meiosis I
Prophase 1
1. Place the chromosomes on a piece of paper. This paper represents a cell.
2. Place the two chromosomes side by side to form a tetrad.
3. Simulate three events of crossing over. Exchange three beads from the
chromatids that are next to each other in the middle of the tetrad (see
* below the chromatids).
4. Draw and color code your new configuration below.
*
*
Metaphase 1 & Anaphase 1
Line up the chromosomes as they should appear in Metaphase 1 (middle of spindle), then
Anaphase 1 (tetrad pulled apart) and draw them below.
Metaphase 1
Anaphase 1
Telophase 1 & Cytokinesis
1. Tear the paper “cell” in half to represent Telophase 1 and Cytokinesis 1.
QUESTIONS:
1. How many chromosomes did you start with? _______
2. How many chromosomes are in each cell when you finish with Meiosis1? ____
Meiosis 2
Interphase
There is no Interphase between the end of Meiosis 1 and start of Meiosis 2.
QUESTION: Why isn’t Interphase needed?
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Prophase
QUESTION: Does crossing over take place again in Prophase 2? Explain your answer.
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Metaphase
Organize the chromosomes in the middle of the spindle.
Anaphase
Untwist the wires showing the separation of the centromere.
Telophase & Cytokinesis
1. Tear the paper in half again so that each wire is in its own quarter paper.
QUESTION:
1. What is the name of a cell with half of the genetic information? _________________
2. Draw the resulting single chromosomes after all of Meiosis is through.
QUESTION: Describe how/why these cells are genetically unidentical and the process that got them
that way. _________________________________________________________________________
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Analysis Questions
These questions are to be answered on your own. If your answers are the same as someone else’s it
will result in a zero for everyone involved.
1.
2.
3.
4.
5.
6.
Which happens first? Sister chromatids separate, or homologous chromosomes separate. EXPLAIN.
Why is it pointless for sister chromatids to cross over?
Between mitosis and meiosis, which is more complicated and why?
After the activity, did you end up with beads of all one color on the wires?
How does this (# 4) relate to real cells/why is it important?
Describe in detail how daughter cells in mitosis are different from the daughter cells of meiosis.