Bio160 Sp20 LM8 Mitosis Meiosis Accessible Gregor-1 PDF

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Biology 160 Lab Module 7: Mitosis and Meiosis Introduction: One main tenet of the cell theory is that “All cells arise from preexisting cells”. This happens through the process of cell division in which new cells are formed when a “parent cell” divides itself into two new “daughter cells”. In prokaryotes and single-celled eukaryotes, cell division is essential for reproduction and continued existence of a species (although the specifics of the process differ somewhat between these two groups of organisms). In multicellular, eukaryotic organisms, cell division is necessary for growth of the organism and for the replacement of damaged or worn out cells. In most Eukaryotic organisms, reproduction is “sexual” meaning that offspring are produced by the union of two sex cells (gametes), specifically an egg cell and a sperm cell. When these two cells unite(fertilization), the resulting cell is called a zygote. This zygote then undergoes many cell divisions (growth) to eventually produce the multicellular offspring. The “life cycle” of a cell may be thought of as being from the time a cell is produced by division of a parent cell until the time it undergoes cell division to produce two new daughter cells. This cycle is called the “cell cycle” and is shown in a diagram in your textbook. The cell cycle is a continuous process but has been divided into different phases by scientists for better understanding of the various events that take place. These phases consist of interphase (including G1, S, and G2), mitosis (division of the nucleus including prophase, metaphase, anaphase, and telophase), and cytokinesis (division of the cytoplasm). In this lab, you will explore both types of cell division: mitosis to create new identical somatic body cells, and meiosis to create a diverse array of gametes for reproduction.

Outcomes: Upon successful completion of this lab, you should be able to: 1. Define/explain each of the following terms: cell cycle, mitosis, cytokinesis, chromosome, DNA, sister chromatid, chromatin, centromere, nuclear membrane, spindle (microtubules), and centrosomes. 2. Demonstrate and explain mitosis using chromosome models. 3. Identify the stages of the cell cycle, including all stages of interphase and the mitotic phase. 4. Distinguish between mitosis & cytokinesis, and identify the processes involved in nuclear & cell division. 5. Understand the regulatory roles of each of the cell cycle checkpoints; a failed check point leads to __. 6. Understand the roles and consequences of failures of oncogenes and tumor-suppressor genes. 7. Distinguish between homologous chromosomes and sister chromatids. 8. Compare and contrast a gamete and a somatic cell. 9. Explain how haploid and diploid cells differ. 10. Identify the process that forms haploid cells, including being able to list in correct order and briefly describe the phases of meiosis. At each phase in meiosis: a. identify the number of chromosomes and chromatids. b. determine if the cells are haploid or diploid. c. list the phase that separate homologous chromosomes. d. list the phase that separate sister chromatids. 11. Explain how crossing-over, independent assortment, and random fertilization contribute to genetic variation in sexually reproducing organisms. 12. Compare and contrast mitosis and meiosis with respect to process and outcomes.

Part 1: Modeling Mitosis and the Cell Cycle Cells do not spend the majority of their time dividing. Most of a cell’s life is spent in interphase. Interphase is an important part of understand how cell division is regulated and controlled.

Step 1: Cell Cycle Access the following url: http://www.hhmi.org/biointeractive/eukaryotic-cell-cycle-and-cancer read the Summary, download the Overview Worksheet, (right side of the screen) and the click on “Start Click and Learn” link to access the interactive lesson on the Eukaryotic Cell Cycle and Cancer. Complete the Overview Worksheet. To save the Overview Worksheet: 1. Complete it by typing your answers into the boxes in the pdf. 2. Chose “Print” 3. Chose Print to pdf instead of sending the document to your printer. (This allows you to save it with your answers!) 4. Name the documents as: YournameLM7S20. 5. Upload that document to the Lab Module 7 canvas assignment. Be sure to upload the LM7 Lab as well.

Step 2a: Connecting the events of Mitosis in visual sequence In this section, you are going to use the marked events unique to each part of Mitosis and Interphase to visually identify & become familiar with the unique sequence of events.

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Each of the cells marked by a capital letter (A-L) is in an identifiable part of the cell cycle. The letter are filled in below. Match the following descriptions to the events. 1. The nuclear envelope reforms, the mitotic ______ is F or J - Late Interphase spindle dissolves. Cytokinesis occurs concurrently. ______ is L, E or I - Prophase (Early or Late) 2. Cytokinesis and mitosis are complete; chromosomes no longer visible. ______ is C – Metaphase 3. Sister chromatids separate as the cell elongates; kinetochore microtubules shorten. 4. DNA has replicated, cell growth is evident. Sister ______ is D or H – Anaphase chromatids exist but are not visible. 5. Nuclear envelope dissolves, mitotic spindle ______ is K & maybe A – Telophase forms, chromosomes appear. 6. Chromosomes line up singly at the central plane of the cell ______ is G or B: Daughter Cells (early Interphase)

Step 2b: Making Model Chromosomes In this section, you are going to build a model cell to walk through mitosis. The point of this is to have TACTILE experience of how the stages work. Here are three options for building models(choose 1): A. Find two colors of yarn, string, pipe cleaner, knex pieces, lincoln log pieces, or other small, linear items you have on hand. You will need 3 different lengths with a pair of colors of each length (e.g., blue & red LONG, blue & red MEDIUM, and blue & red SHORT). B. Print out Appendix A (below) and cut out the model chromosomes; the black & white set is for Mitosis, the 3rd set of images is in homologous pairs for Meiosis. C. If you don’t have household items or a computer printer, then cut out and color strips of paper to match the model chromosomes shown in Appendix A (below).

Step 2c: Instructions: Link to mitosis diagram in your book Vocabulary List: cell cycle, mitosis, cytokinesis, chromosome, DNA, sister chromatid, chromatin, centromere, nuclear membrane, spindle (microtubules), and centrosomes. 1) Using the model chromosomes (from Step 2a), set up a mock cell in G1 phase. a) Draw or add a photo of your model to show the pairs of UNREPLICATED homologous chromosomes. Label one color “from mom” the other color “from dad”. Are there sister chromatids? Explain. b) [Insert labeled and explained G1 phase photo/drawing here] 2) Change the mock cell so that it models the end of S phase. a) Draw or take a photo of your model to show a pair of REPLICATED homologous chromosomes. Label at least one centromere. Are there sister chromatids? Explain. b) [Insert labeled S phase photo/drawing here] 3) Go online and find a microscope image of prophase.

a) Change your mock cell so that it models prophase as shown in the microscopic image. b) Draw or take a photo of your model to the prophase cell. Why is it hard to distinguish chromosomes? Explain. Is the DNA in this cell already replicated? c) [Insert labeled prophase photo/drawing here] 4) Go online and find a microscope image of metaphase. a) Change your mock cell so that it models metaphase as shown in the microscopic image. b) Draw or take a photo of your model to the metaphase cell. Described how your model differs from the microscopic image you found online. How many chromosomes are in this metaphase cell? Explain. c) [Insert labeled metaphase photo/drawing here] 5) Go online and find a microscope image of anaphase. a) Change your mock cell so that it models anaphase as shown in the microscopic image. b) Draw or take a photo of your model to the anaphase cell. Label: chromosome, spindle, and centrosomes in your photo/drawing. How many chromosomes are in this anaphase cell? Explain. c) [Insert labeled anaphase photo/drawing here] 6) Go online and find a microscope image of telophase/cytokinesis. a) Change your mock cell so that it models telophase/cytokinesis as shown in the microscopic image. b) Draw or take a photo of your model to the telophase/cytokinesis cell. Label: chromosomes/chromatin, nuclear membranes, and centrosomes in your photo/drawing. How many chromosomes are in this telophase/cytokinesis cell? Explain. c) [Insert labeled anaphase photo/drawing here]

Step 3: Questions Now that you have modeled the process, test your knowledge below: 1) What role does mitosis play in an adult human like yourself? 2) How is cytokinesis different between plants and animals (put another way, why can’t plant cells undergo cytokinesis in the same way animal cells do)?

Part 2: Somatic Cell Cycle Phases in Onion Root Tip Microscopic Image

One the image above, identify the mitotic stages of the 20 boxed cells as interphase, prophase, metaphase, anaphase, telophase or two daughter cells. It might help to magnify the image on your computer screen. If you aren’t sure of the phase (because these will be judgement calls) explain your reasoning (e.g. this is either anaphase or telophase. I said anaphase because…). .

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Part 3: Modeling Meiosis: Link to your books’ Meiosis diagram Introduction As shown in this flowchart, genes in chromosomes are transmitted from a child’s parents via an egg and a sperm to the zygote, which is a fertilized egg. The zygote contains all the chromosomes that were in the sperm and the egg.

In humans, each egg and each sperm has 23 chromosomes. Therefore, the zygote has _____ chromosomes, and each cell in the embryo and child has _____ chromosomes.

3a: How Meiosis Makes Haploid Gametes Before meiosis, the cell makes a copy of the DNA in each chromosome. The two copies of the DNA in each chromosome are condensed into sister chromatids. Then, there are two cell divisions, Meiosis I and Meiosis II.

This figure shows meiosis for a cell with a single pair of homologous chromosomes. One of the chromosomes has striped chromatids to indicate that the alleles for many of the genes are different in these two chromosomes.

At the beginning of Meiosis I, the two homologous chromosomes line up next to each other. Then, the homologous chromosomes are separated into two daughter cells. These daughter cells have half as many chromosomes as the parent cell, so the daughter cells are haploid. In Meiosis II, the sister chromatids of each chromosome are separated. Meiosis II produces four haploid daughter cells, the gametes.

Simulating Meiosis: Visit this site: LINK from Rutgers University Read the Rutgers introduction and answer the following questions. 1) What kind of cell does meiosis occur in? 2) What does diploid mean? 3) Why do gametes need to be haploid? 4) How does meiosis create haploid gametes? 5) Match each item in the list on the left with the appropriate match from the list on the right. Meiosis I separates _____ a. pairs of homologous chromosomes Meiosis II separates _____ b. sister chromatids Mitosis separates _____ In the Rutgers meiosis website, click “Begin Assignment”. Part I asks you to review the stages of meiosis from your textbook. Use diagram 7.6 in your textbook (click this LINK) to draw and/or briefly describe the phases of meiosis below. You can also make your own drawing on another sheet, take a picture, and paste in this document in place of the table.

In the Rutgers meiosis website, click “Begin Part II”. Click “Click here to begin” Read the Part II instructions and complete the Meiosis I section, document this by sketching what the plant sex cells look like at each of the stages you identified. You can also make your own drawing on another sheet, take a picture, and paste in this document in place of the table.

Repeat the process with the Meiosis II cells, document by sketching what the plant sex cells look like at each of the stages you identified. You can also make your own drawing on another sheet, take a picture, and paste in this document in place of the table.

In the Rutgers meiosis website, click “Begin Part 4” (really it takes you to part III it’s a typo in the module). Complete the THREE case studies of the cytogeneticists. Record the gender/ karyotype and the diagnosis for each case studies. Case # _____: Sex Chromosomes_______ karyotype:________________ Diagnosis description: Case # _____: Sex Chromosomes_______ karyotype:________________ Diagnosis description: Case # _____: Sex Chromosomes_______ karyotype:________________ Diagnosis description:

3b: Unique Events of Meiosis (How Crossing Over and Independent Assortment Impact Gamete Variety) To begin, you will model meiosis with this pair of model chromosomes. A person with chromosomes with these alleles would have the genotype AaSs.  Use your pair of model chromosomes to model each step of meiosis. Use string to model the cell membranes at each stage. 7) 1a. Show the results of your modeling in this figure. Sketch and label the chromosomes in each cell that is produced by Meiosis I and by Meiosis II. 8) 9) 1b. Which combinations of alleles are observed in the different gametes? 10)

When a pair of homologous chromosomes is lined up next to each other during Meiosis I, the two homologous chromosomes can exchange parts of a chromatid. This is called crossing over. 2. On each chromatid of the chromosomes in the bottom row of this figure, label the alleles for the Aa and Ss genes. The bottom row of this figure shows how the homologous chromosomes separate during Meiosis I. Then, the sister chromatids will separate during Meiosis II. This will produce gametes with four different combinations of the alleles for these two genes. 3. The combinations of alleles in the different gametes will be:

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Next, you will model meiosis using two pairs of homologous chromosomes. At the beginning of Meiosis I each pair of homologous chromosomes lines up independently of how the other pair of homologous chromosomes has lined up. As shown in the chart below, at the beginning of Meiosis I the as chromosome can be lined up on the same side as either the l chromosome or the L chromosome. This is called independent assortment.  Use your four model chromosomes to model Meiosis I and Meiosis II for both of the possible ways of lining up the model chromosomes at the beginning of Meiosis I. 4. Record the results of your modeling in this chart.

5. The bottom row of this chart shows that meiosis with independent assortment can produce gametes with four different combinations of the alleles for these three genes. Crossing over would result in gametes with four additional combinations of alleles. List the additional combinations of alleles that could be produced by crossing over.

These results show that independent assortment and crossing over can produce gametes with eight different combinations of the alleles for these three genes. This represents only a tiny portion of the genetic diversity of the gametes produced by a single person. Since human cells have 23 pairs of homologous chromosomes, independent assortment alone can produce more than 8 million different combinations of chromosomes in the gametes produced by one person! Crossing over produces substantial additional genetic diversity.

Appendix A Printable chromosomes (Mitosis)...