Modeling Meiosis



Biology, 6th Period


February 13, 2000


Purpose:


To model the process of Meiosis (Meiosis I; Prophase I, Metaphase I, Anaphase I, Telophase I, and Cytokinesis I, and Meiosis II; Prophase II, Metaphase II, Anaphase II, Telophase II, and Cytokinesis II) with use of actual material, rather than drawings, listed below.


Materials:



o (4) Pieces of string (1m)
o (4) Pieces of string (40cm)
o (4) Strips (2cm X 6cm) of paper:

o (1) Light blue
o (1) Dark Blue
o (1) Light Green
o (1) Dark Green
o Scissors
o (8) Paper clips
o Metric Ruler
o Transparent tape
o (8) Pieces of string (10cm)
Procedure:



o Using a 1m piece of string, make a circle on your desk to represent the cell/plasma membrane of a cell. Using a 40cm piece of string, make another circle inside the cell to represent the nuclear membrane.
o Fold each of four strips of paper in half, lengthwise. Then place one strip of each color inside the nucleus to represent a chromosome before replication. The light and dark strips of the same color represent homologous chromosomes. The light-colored strips represent chromosomes from the other parent.
o Interphase. To represent DNA replication, unfold each paper clip and cut each half, lengthwise. The two resulting pieces represent chromatids. Attach the two identical chromatid strips at the center with a paper clip so an X is formed. Each paper clip represents a centromere.

o What process did you model when you cut the paper strips in half?
· I modeled S Phase (Synthesis). This includes the duplication of the original DNA.




o What is the function of the centromere?
· The centromere’s function is to hold each chromatid in place. Also, the kinetochore is located in the centromere. Therefore, another function of the centromere may be to house the kinetochore.

Meiosis I

o Prophase I. Remove the nuclear membrane. Please the blue chromosomes side by side. Do the same for the green chromosomes. Simulate crossing over by measuring and cutting a 2cm tip from the light blue strip. Do the same with a dark blue strip. Tape the light blue tip to the dark blue strip, and tape the dark tip to the light blue strip. Do the same for the green strips.
A. What is the purpose of placing the light and dark strips of the same color side by side?


· Placing the light and dark strips of the same color side by side accomplishes full representation of homologous chromosomes from 2 (Blue and Green) parents. Also, in this procedure, the event of crossing over occurs. In order to achieve a “correct” crossing over procedure, portions of chromatids break off and attach to adjacent chromatids on the homologous chromosomes.


5. Metaphase I. Place four 10cm strings inside the cell, so that two strings extend from one side into the center of the cell and two strings extend from the opposite side into the center of the cell. The strings represent spindle fibers. Attach a string to the centromere of each chromosome (chromatid pair) with tape. Move the chromosomes to the center of the cell. Note: Make sure that the strings attached to similar colors come from opposite sides of the cell.


6. Anaphase I. Gather the lose ends of the strings on both sides of the cell, and pull the strings in opposite directions.


7. Telophase I. Untape the string from each centromere. Place a 40cm piece of string around each group of chromatids, forming two nuclei. Place a 1m piece of string around each cell, forming two cell membranes.


A. How many chromosomes are in each cell? Describe what each part represent.


· There are 2 chromosomes in each cell. The 40cm string represents two nuclei, the 1m strings represent two cell membranes, and the paper clips represent centromeres.


Meiosis II


8. Prophase II. Remove the strings that represent the nuclear and cell membranes in both cells. Attach a 10cm piece of string to each chromatid.


A. What must happen to the centromeres before the chromatids can separate?


· The centromeres must separate from there chromatids, before the chromatids can separate.


9. Metaphase II. Move the chromosomes to the center of each cell. Make sure that the strings attached to the two strips in each chromosome come from opposite sides of the cell.


10. Anaphase II. Gather the