How to Proceed
- Read through the introductory materials below.
- Open the Unit 4 Experiment Answer Sheet and complete the following Experiment exercises this unit:
- Experiment 4 Exercise 1 – Mitosis in a Plant Cell (~45 min)
- Experiment 4 Exercise 2 – Meiosis (~30 min)
- Experiment 4 Exercise 3 – Karyotyping (~60 min)
- Save your completed Unit 4 Experiment Answer Sheet and submit it no later than Sunday midnight (CT).
Mitosis – Introduction
The life cycle of a typical cell is roughly divided into two phases, Interphase and Cell Division. Interphase is a time of growth and synthesis and is further divided in to G1, S and G2 stages. G stands for “growth”. During G1, the cell grows and makes materials needed to replicate its DNA. DNA is then replicated during the S or “synthesis” phase. Additional growth occurs during G2 as the cell prepares for cell division. Cell division encompasses both nuclear division (Mitosis) and cytoplasm division (Cytokinesis). See Fig 8.6 on p 125 in your book.
Mitosis allows cells in our body to regenerate (e.g., replacement of shed skin cells) and to repair damaged tissue, since mitosis produces daughter cells that are identical to the parent cell. Before beginning this exercise, you will want to review Mitosis in our online lecture and examine the diagrams in Fig 8.7 on pp 126-127 and Fig 8.8 on p 128, which illustrates some differences between animal and plant cells. As you can see, each phase of the cell cycle can be recognized based on the appearance the chromosomes and nucleus. In this first exercise, you will need to be able to identify the various phases of the cell in onion cells. Below is an example of what you will be looking at:
From: Ackroyd, Miller and Sauriol. No date. Mitotic cell division in onion root tip, Allium cepa.
| Slide # |
Phase |
Description |
| 1-2 |
Interphase |
Chromosomes are not visible in the nucleus (gray circle). |
| 3-5 |
Prophase |
Chromosomes have become visible; although not apparent, the nuclear membrane is breaking down. |
| 6 |
Metaphase |
Chromosomes have aligned along the equator (mid-line). |
| 7-8 |
Anaphase |
Sister chromatids have separated and are being pulled to opposite poles. |
| 9-10 |
Telophase |
Chromosomes are clumped at opposite poles, the nucleus has reformed and a cell plate is forming. |
Note that is hard to determine exactly when one phase ends and the next one starts. Slide #7, for example is early anaphase and could also be considered late metaphase. Slide #9 is early telophase, but might also be considered late anaphase.
See your Unit 4 Experiment Answer Sheet for the instructions and the photographs you will use to complete this exercise.
Meiosis – Introduction
Meiosis is the process by which gametes (eggs and sperm) are produced from a germ cell. This type of cell division is unlike mitosis in that the cells produced are genetically different than the parent cell and the resulting cells contain only half the number of chromosomes (haploid). In this exercise, you will need to demonstrate your understanding of Meiosis and the role it plays in sexually reproducing organisms. Review this unit’s reading in your book (pp 131-141) and this unit’s online lecture before completing this exercise. You will need to review the following animation, so be sure that you are able to open and view it:
McGraw-Hill Higher Education. 2006. How Meiosis Works
http://highered.mcgraw-hill.com/sites/0072495855/student_view0/chapter28/animation__how_meiosis_works.html (Links to an external site.)
When you are ready, open the Unit 4 Experiment Answer Sheet and answer the questions for this exercise.
Karyotyping – Introduction
Review pp 130-121, pp 138-140 and our online lecture this unit before beginning this exercise. Many genetic disorders arise as a result of errors during Meiosis and the formation of gametes (= egg and sperm). Frequently, these errors are due to non-disjunction, in which chromosomes fail to separate correctly during Anaphase. When this happens, a daughter cell ends up with either an extra chromosome or it is missing a chromosome. These genetic disorders can be detecting using a screening process called a karyotype. In this exercise, you will learn how a karyotype is generated and used to diagnose the presence or absence of a disorder.
You will use the following website to complete this exercise:
The Biology Project. 1998. Karyotyping Activity
http://www.biology.arizona.edu/human_bio/activities/karyotyping/karyotyping.html V
WEEK 4 EXPERIMENT ANSWER SHEET Please submit to the Week 4 Experiment dropbox no later than Sunday midnight.
SUMMARY OF ACTIVITIES FOR WEEK 4 EXPERIMENT ASSIGNMENT
· Experiment 4 Exercise 1 –Mitosis in a Plant Cell
· Experiment 4 Exercise 2 – Meiosis
· Experiment 4 Exercise 3 – Karyotyping
Experiment 4 Exercise 1: Mitosis in a Plant Cell
Read through the Experiment 4 Introduction material before starting. In this exercise we will look at the different stages of mitosis in onion cells. The length of the cell cycle in the onion root tip is about 24 hours, but mitosis only occupies only one to two hours.
Procedure
A. Review the information on p 125 in your book and record your predictions as to the percentage of cells you expect to see in each of the phases of the cell cycle in Table 1 (after the photographs).
B. In the four photographs below, examine each cell indicated by a red dot. There are a total of 65 cells that need to be examined. Determine how many cells are in the various stages of the Cell Cycle. Refer to your book and the Experiment 4 Introduction information for help determining the cell cycle stages.
C. Enter your data in Table 1. Note that the “Calculated %” is equal to the Number of cells in stage / Total cells counted x 100.
D. Answer the questions that follow.
Table 1: Predictions and actual number of cells observed in each stage of the cell cycle (2 pts)
| Stage |
Predicted % |
Number of Cells |
Total Cells Counted |
Calculated % |
| Interphase |
|
|
65 |
|
| Prophase |
|
|
65 |
|
| Metaphase |
|
|
65 |
|
| Anaphase |
|
|
65 |
|
| Telophase |
|
|
65 |
|
| Total |
100% |
65 |
65 |
100% |
Questions
1. What stage of the cell cycle were most of the onion root tip cells in (1 pts)?
Is this what you would expect based on what you’ve read this week; why or why not? Cite source(s) used (1 pts).
2. How accurate were your predictions, based on your data, for each stage of the cell cycle (1 pts)?
3. What is the function of mitosis in an organism such as a human? Cite source(s) used (2 pts).
Experiment 4 Exercise 2: Meiosis
Review this week’s reading in your book (pp 131-141) and this week’s online lecture. Then view the following animation before answering the questions below; be sure your audio is on:
McGraw-Hill Higher Education. 2006. How Meiosis Works http://highered.mcgraw-hill.com/sites/0072495855/student_view0/chapter28/animation__how_meiosis_works.html
Questions
1. Why is it necessary to reduce the chromosome number in gamete cells (egg and sperm), but not other cells of an organism? Cite source(s) used (2 pts).
2. Describe at least two differences between Meiosis I and Meiosis II in terms of what is produced and what occurs with the chromosomes. Cite source(s) used (2 pts).
3. If humans have 46 chromosomes in each of their body cells, determine how many chromosomes you would expect to find in the following cells (4 pts):
Sperm _________
Liver cell _________
Daughter cell from mitosis _________
Daughter cell from Meiosis II _________
4. _____ are separated during Meiosis I, while _____ are separated during Meiosis II (2 pts).
a. Sister chromatids, sex chromosomes
b. Sister chromatids, homologous chromosomes
c. Homologous chromosomes, sister chromatids
d. Sex chromosomes, sister chromatids
5. At the beginning of meiosis I, cells are ____ and at the beginning of meiosis II, they are ____ (2 pts).
a. Diploid, diploid
b. Diploid, haploid
c. Haploid, haploid
d. Haploid, diploid
Experiment 4 Exercise 3: Karyotyping
Go to the following website:
The Biology Project. 1998. Karyotyping Activity
http://www.biology.arizona.edu/human_bio/activities/karyotyping/karyotyping.html
Procedure
A. Read over the material on the first page and then click on Patient Histories (at the bottom of the page).
B. Click on Complete Patient A’s Karyotype. Note a single chromosome located to the left of the paragraph at the top. You need to match this chromosome with the appropriate pair.
a. Some of the chromosomes arranged beneath the paragraph are hyperlinked (have a blue line beneath them).
b. Click on the hyperlink associated with the matching chromosome.
C. Record in Table 2 below the correct match for this first chromosome (a).
D. Continue until you have matched all chromosomes required. Note that the letters (a-e) correspond to the order that the chromosomes are presented.
Table 2. Patient A karyotype data (1 pts).
| Chromosome Presented |
Matches # |
| Chromosome a |
|
| Chromosome b |
|
| Chromosome c |
|
| Chromosome d |
|
| Chromosome e |
|
Questions
1. What notation would you use to characterize Patient A’s karyotype? Be sure to read over the information presented so you know the correct notation format (1 pts).
2. Based on the table of possible chromosomal disorders displayed on the website, what diagnosis would you give patient A (1 pts)?
3. When during Meiosis does the error occur that results in this karyotype; be specific (1 pts)?
Procedure (continued)
E. Click on the Patient History button (bottom of the page) and then click on Complete Patient B’s Karyotype.
F. Match the chromosomes presented as done in the previous exercise.
G. Fill in the Table 3 below, indicating how you matched up the chromosomes presented with the actual chromosomes in the karyotype.
Table 3. Patient B karyotype data (1 pts).
| Chromosome Presented |
Matches # |
| Chromosome a |
|
| Chromosome b |
|
| Chromosome c |
|
| Chromosome d |
|
| Chromosome e |
|
| Chromosome f |
|
| Chromosome g |
|
| Chromosome h (This is a tough one) |
|
Questions
4. What notation would you use to characterize Patient B’s karyotype (1 pts)?
5. What diagnosis would you give patient B (1 pts)?
6. Why does this individual exhibit male characteristics and not female? Cite your source (2 pts).
Procedure (continued)
H. Click on the Patient History button (at the bottom) and then click on Complete Patient C’s Karyotype.
I. Match the chromosomes presented as done in the previous exercise.
J. Fill in Table 4 below, indicating how you matched up the chromosomes presented with the actual chromosomes in the karyotype.
Table 4. Patient C karyotype data (2 pts).
| Chromosome Presented |
Matches # |
| Chromosome a |
|
| Chromosome b |
|
| Chromosome c |
|
| Chromosome d |
|
| Chromosome e |
|
| Chromosome f |
|
| Chromosome g |
|
| Chromosome h |
|
| Chromosome i |
|
Questions
7. What notation would you use to characterize Patient B’s karyotype (1 pts)?
8. What diagnosis would you give patient C (1 pts)?
9. Why might the risk of this disorder increase as a woman gets older? Cite any sources used (3 pts).
Week 4 Experiment Grading Rubric
| Component |
Expectation |
Points |
| Experiment 4 Exercise 1 |
Distinguishes among the various stages of the cell cycle and correctly answers the questions (Table 1, Questions 1-3). |
7 pts |
| Experiment 4 Exercise 2 |
Demonstrates an understanding of meiosis and how it relates to sexual reproduction (Questions 1-6). |
12 pts |
| Experiment 4 Exercise 3 |
Creates and uses a karyotype to diagnose genetic disorders (Tables 2, 3, and 4; Questions 1-9). |
16 pts |
| TOTAL |
|
|
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