INSTRUCTIONS:

·         On your own and without assistance, complete this Lab 5Answer Sheet electronically and submit it via the Assignments Folder by the date listed intheCourse Schedule (under Syllabus).

·         To conduct your laboratory exercises, use the Laboratory Manual located under Course Content. Read the introduction and the directions for each exercise/experiment carefully before completing the exercises/experiments and answering the questions.

·         Save your Lab 5Answer Sheet in the following format:  LastName_Lab5 (e.g., Smith_Lab5).

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Pre-Lab Questions

1. Compare and contrast mitosis and meiosis.

1.  What major event occurs during interphase?

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. 10 beads should be used to create each individual sister chromatid (20 beads per chromosome pair). Two five-holed beads represent each centromere. To do this…

1. Start with 20 beads of the same color to create your first sister chromatid pair. Five beads must be snapped together for each of the four different strands. Two strands create the first chromatid, and two strands create the second chromatid with a 5-holed bead at the center of each chromatid.  This creates an “I” shape.
2. Connect the “I” shaped sister chromatids by the 5-holed beads to create  an “X” shape.
3. Repeat this process using 20 new beads (of a different color) to create the second sister chromatid pair.
1. Assemble a second pair of replicated sister chromatids; this time using 12 beads, instead of 20, per pair (six beads per each complete sister chromatid strand).
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 phase.

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 1 – Meiotic Division Beads Diagram

Prophase I

Metaphase I

Anaphase I

Telophase I

Prophase II

Metaphase II

Anaphase II

Telophase II

Cytokinesis

Part 2: Modeling Meiosis with Crossing Over

1. Build a pair of replicated, homologous chromosomes. 10 beads should be used to create each individual sister chromatid (20 beads per chromosome pair). Two five-holed beads represent each centromere. To do this…
1. a. Start with 20 beads of the same color to create your first sister chromatid pair. Five beads must be snapped together for each of the four different strands. Two strands create the first chromatid, and two strands create the second chromatid with a 5-holed bead at the center of each chromatid.  This creates an “I” shape.
2. Connect the “I” shaped sister chromatids by the 5-holed beads to create  an “X” shape.
3. Repeat this process using 20 new beads (of a different color) to create the second sister chromatid pair.
2. Assemble a second pair of replicated sister chromatids; this time using 12 beads, instead of 20, per pair (six beads per each complete sister chromatid strand). Snap each of the four pieces into a new five-holed bead to complete the set up.
3. Pair up the homologous chromosomes created in Step 8 and 9.
4. SIMULATE CROSSING OVER. To do this, bring the two homologous pairs of sister chromatids together (creating the chiasma) and exchange an equal number of beads between the two. This will result in chromatids of the same original length, there will now be new combinations of chromatid colors.
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 Part1 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

Post-Lab Questions

1.      What is the ploidy of the DNA at the end of meiosis I? What about at the end of meiosis II?

2.      How are meiosis I and meiosis II different?

3.      Why do you use non-sister chromatids to demonstrate crossing over?

4.      What combinations of alleles could result from a crossover between BD and bd chromosomes?

5.      How many chromosomes were present when meiosis I started?

6.      How many nuclei are present at the end of meiosis II? How many chromosomes are in each?

7.      Identify two ways that meiosis contributes to genetic recombination.

8.      Why is it necessary to reduce the number of chromosomes in gametes, but not in other cells?

9.      Blue whales have 44 chromosomes in every cell. Determine how many chromosomes you would expect to find in the following:

Sperm Cell:

Egg Cell:

Daughter Cell from Mitosis:

Daughter Cell from Meiosis II:

10.  Research and find a disease that is caused by chromosomal mutations. When does the mutation occur? What chromosomes are affected? What are the consequences?

11.  Diagram what would happen if sexual reproduction took place for four generations using diploid (2n) cells.

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

Post-Lab Questions

1.      Record your hypothesis from Step 1 in the Procedure section here.

2.      What do your results indicate about cell cycle control?

3.      Suppose a person developed a mutation in a somatic cell which diminishes the performance of the body’s natural cell cycle control proteins. This mutation resulted in cancer, but was effectively treated with a cocktail of cancer-fighting techniques. Is it possible for this person’s future children to inherit this cancer-causing mutation? Be specific when you explain why or why not.

4.      Why do cells which lack cell cycle control exhibit karyotypes which look physically different than cells with normal cell cycle.

5.      What are HeLa cells? Why are HeLa cells appropriate for this experiment?