Experiment 1: Following Chromosomal DNA Movement through Meiosis

In this experiment, you will model the movement of the chromosomes through meiosis I and II to create gametes.

Procedure:

Part 1: Modeling Meiosis without Crossing Over

As prophase I begins, the replicated chromosomes coil and condense…

1. Build a pair of replicated, homologous chromosomes (Figure 3). One pipe cleaners should be used to create each individual sister chromatid (2 pipe cleaners per chromosome pair). One bead represents each centromere. To do this…

1. Start with two pipe cleaners of the same color to create your first sister chromatid pair. Hold the pipe cleaners next to each other and string the pipe cleaners through one bead. Slide the bead halfway down the pipe cleaners. Then, pull bottom ends of the pipe cleaners away from each other to create an "X" shape.
2. Repeat this process using the other two matching pipe cleaners to create the second sister chromatid pair.
1. Cut the two remaining pipe cleaners in half. Repeat step 1 using the two pipe cleaner halves of the same color to create homologous chromosomes (Figure 4).
2. Pair up the homologous chromosome pairs created in Step 1 and 2. DO NOT SIMULATE CROSSING OVER IN THIS TRIAL. You will simulate crossing over in Part 2.
3. Configure the chromosomes as they would appear in each of the stages of meiotic division (prophase I and II, metaphase I and II, anaphase I and II, telophase I and II, and cytokinesis).
4. Diagram the corresponding images for each stage in the sections titled "Trial 1 – Meiotic Division Beads Diagram." Be sure to indicate the number of chromosomes present in each cell for each phase.

Part 1 – Meiotic Division Beads Diagram

Prophase I

Metaphase I

Anaphase I

Telophase I

Prophase II

Metaphase II

Anaphase II

Telophase II

Cytokinesis

1. Disassemble the beads used in Part 1. You will need to recycle these beads for a second meiosis trial in Steps 8 – 13.

Part 2: Modeling Meiosis with Crossing Over

1. Build a pair of replicated, homologous chromosomes. One pipe cleaners should be used to create each individual sister chromatid (two pipe cleaners per chromosome pair). One bead represents each centromere. To do this…
   1. Start with two long pipe cleaners of the same color to create your first sister chromatid pair. Hold the pipe cleaners next to each other and string the pipe cleaners through one bead. Slide the bead halfway down the pipe cleaners. Then, pull bottom ends of the pipe cleaners away from each other to create an "X" shape.
   2. Repeat this process using the two remaining long pipe cleaners to create the second sister chromatid pair.
2. Assemble a second pair of replicated sister chromatids, this time using the pipe cleaners you cut in Part 1. Use the two pipe cleaner halves of the same color for each homologous chromosome.
3. Pair up the homologous chromosomes created in Step 8 and 9.
4. SIMULATE CROSSING OVER. To do this, bring two chromatids from the two homologous pairs of sister chromatids together (creating the chiasma) and use your scissors to cut the pipe cleaners at the chiasma. Exchange and connect the pipe cleaner pieces by twisting the ends of the pieces around the different colored pipe cleaner. This will result in chromatids of the same original length, there will now be new combinations of chromatid colors (Figure 5). Do this for both sets of homologous chromosomes.
5. Configure the chromosomes as they would appear in each of the stages of meiotic division (prophase I and II, metaphase I and II, anaphase I and II, telophase I and II, and cytokinesis).
6. Diagram the corresponding images for each stage in the section titled "Trial 2 – Meiotic Division Beads Diagram." Be sure to indicate the number of chromosomes present in each cell for each phase. Also, indicate how the crossing over affected the genetic content in the gametes from Part 1 versus Part 2.

Part 2 – Meiotic Division Beads Diagram:

Prophase I

Metaphase I

Anaphase I

Telophase I

Prophase II

Metaphase II

Anaphase II

Telophase II

Cytokinesis

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Experiment 2: The Importance of Cell Cycle Control

Some environmental factors can cause genetic mutations which result in a lack of proper cell cycle control (mitosis). When this happens, the possibility for uncontrolled cell growth occurs. In some instances, uncontrolled growth can lead to tumors, which are often associated with cancer, or other biological diseases.

In this experiment, you will review some of the karyotypic differences which can be observed when comparing normal, controlled cell growth and abnormal, uncontrolled cell growth. A karyotype is an image of the complete set of diploid chromosomes in a single cell.

Procedure

1. Begin by constructing a hypothesis to explain what differences you might observe when comparing the karyotypes of human cells which experience normal cell cycle control versus cancerous cells (which experience abnormal, or a lack of, cell cycle control). Record your hypothesis in Post-Lab Question 1.

   Note: Be sure to include what you expect to observe, and why you think you will observe these features. Think about what you know about cancerous cell growth to help construct this information

2. Go online to find some images of abnormal karyotypes, and normal karyotypes. The best results will come from search terms such as “abnormal karyotype”, “HeLa cells”, “normal karyotype”, “abnormal chromosomes”, etc. Be sure to use dependable resources which have been peer-reviewed
3. Identify at least five abnormalities in the abnormal images. Then, list and draw each image in the Data section at the end of this experiment. Do these abnormalities agree with your original hypothesis?

Hint: It may be helpful to count the number of chromosomes, count the number of pairs, compare the sizes of homologous chromosomes, look for any missing or additional genetic markers/flags, etc.

Data

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