Modeling Mitosis & Meiosis PDF

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Summary

Learning Objectives:
• Understand the cell cycle, its stages, and what happens in each stage.
• Understand why your body’s cells complete mitosis and meiosis.
• Be able to demonstrate the processes of mitosis and meiosis.
• Know the differences between mitosis, meiosis I, and...

Description

Modeling Mitosis & Meiosis Learning Objectives:     

Understand the cell cycle, its stages, and what happens in each stage. Understand why your body’s cells complete mitosis and meiosis. Be able to demonstrate the processes of mitosis and meiosis. Know the differences between mitosis, meiosis I, and meiosis II. Know what a karyotype is and how it is used to diagnose medical conditions.

Part I: The Cell Cycle You will need your notes from the cell reproduction lecture to complete this lab. Please use terms from the lecture, not terms you found on the internet. 1) What are the stages of the cell cycle? Hint: There are 4, and they can be listed as a single letter with or without a number. G1, S, G2, M 2) At what stage does the DNA duplicate? DNA duplicates in S stage. 3) When, in the cycle, does mitosis occur? Mitosis occurs when the interphase ends. 4) Give some examples of how the cell cycle differs for different types of cells. For example, how is it different between skin versus brain cells. As an example, in plant cells the cell plate just expands and each new cell creates individual cell walls, while in animal cells there is a ring that contracts and eventually the cytoplasm just partitioned. 5) When/why does your body need to do mitosis? Mitosis happens when our bodies are growing, so cells need to be duplicated, or when cells die, because the body need new cells to replace the dead ones. 6) When/why does your body need to do meiosis? Meiosis exists during reproduction with the help of sexually reproducing organs, because meiosis implies the

Part II: Mitosis

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Go to https://www.youtube.com/watch?v=N97cgUqV0Cg and watch the “Actual Footage of Cell Division (Kidney Cells)” video

7) What cellular structures are dyed red? Red structures are chromosomes. 8) What cellular structures are dyed green? The green structure is centriole. 9) Describe what is happening to the red structures. First this happens, then this happens, etc… So in that video, we can see one cell that goes through stages: first it is prophase, then it is metaphase, then goes anaphase, then telophase, and the last is cytokinesis. In this part of the lab, you’re going to demonstrate the process of mitosis using socks. You need 6 pairs of socks, with each pair knotted or attached to each other in the middle. Each sock is one molecule of DNA that is joined to another sock, a cloned copy of DNA.

Place your 6 pairs of socks onto a table, jumbled, and take a photo. This is Prophase. Attach the photo to this lab or in the space below. If you attach the photos, be sure the stages are labeled so that I know which you are demonstrating. 10) Prophase:

Line your 6 pairs of socks in a line such that the tips of the chromosomes are touching the ones above and below. So, the toes of your socks should be touching the tops of the socks above it. This is Metaphase. Attach a photo to this lab or in the space below. 11) Metaphase:

Separate each pair of socks and move one of the pair to the far right and another to the far left. In the end you should have 6 socks together on the right and 6 socks together on the left. This is Anaphase and moving into Telophase. Attach a photo to this lab or in the space below.

12) Anaphase:

Questions about mitosis: 13) How many chromosomes did you start with in your cell before running the sock demonstration? 6 chromosomes with duplicated DNA 14) How many chromosomes does each cell have after the demonstration? 3 chromosomes with duplicated DNA 15) What happened during the cell cycle so that when the cell divided in half, it still retained its chromosome number in each of the new cells? During this process the cell duplicates all of its content so the number of chromosomes will be the same. 16) What moved the chromosomes to the equators and pulled them apart at the Metaphase plate? It’s the microtubules and proteins that extend from centrioles and pull chromosomes apart. 17) What is the name of the final process that makes 1 cell into 2 separate cells? Hint: Use your lecture notes.

It’s the anaphase stage.

Part III: Meiosis Meiosis is the formation of gametes (specialized sex cells such as an egg or sperm) that have half the number of chromosomes than other body cells in the organism. Meiosis literally means “to make smaller.” 18) Why would sex cells need half the number of chromosomes? Because sex cells contain only half of the chromosomes as they carry mother’s and father’s genetic information.

To illustrate your understanding of meiosis, you are going to hand draw it onto paper or a white board, take photos, and submit them. You need to start your cell with 6 chromosomes with duplicated DNA. You will need to use 2 different colored markers or pen for this demonstration. To make your 6 chromosomes, draw “X’s” with 2 of each “X” as the same size, but different colors. Here is what it should look like:

X, X

X, X X, X

The red “X’s” represent chromosomes that came originally from the egg, and the green “X’s” originally came from the sperm that created the organism (one from each parent). The size difference represents that each set (pair) of chromosomes is unique, and since they all have differing numbers of genes on them, they are differently sized. Now you will hand draw onto paper or a white board these same chromosomes and their corresponding colors for each of the phases listed below.

Begin by placing all 6 “X’s” into a group in the center of a cell. Since you are drawing by hand, be sure to draw the nucleus surrounding the chromosomes, the centrioles, and the spindle fibers

when needed. This is Prophase I. Take a photo and attach the photo to this lab or in the space below. If you attach the photos, be sure the stages are labeled so that I know which you are demonstrating. If it is easier, you can attach one photo with a progression of steps on the same drawing, like a flow chart. 19) Prophase I, demonstrating the start of crossing over:

Now line the chromosomes up in the middle, demonstrating independent assortment and crossing over. Throughout the rest of these drawings, use the same look for each new chromosome. For example, keep the size and color differentiation as well as maintaining which chromosomes are a combo of green and red. Remember, only a small piece is swapped with crossing over, not an entire strand of DNA or large segment of the DNA. Just swap near the head or the foot of a chromosome. This is Metaphase I once they are lined up in pairs in the center. Be sure that for Metaphase I, they are drawn with pairs similar to those I made on the previous page. Attach a photo to this lab or in the space below. 20) Metaphase I:

Separate your chromosome pair by moving one entire chromosome (with duplicated DNA) to one pole and its partner to the opposite pole. Don’t forget to draw the centrioles and spindle fibers. This is Anaphase I. Attach a photo to this lab or in the space below. 21) Anaphase I:

Draw the nucleus around each set of chromosomes. You should now have 1 large cell drawn with 2 nuclei, each with 3 chromosomes in it. This is Telophase I. Attach a photo to this lab or in the space below. 22) Telophase I:

Your cell has now finished splitting into 2 cells. You will now demonstrate Meiosis II with each cell and include both cells in your drawings. This is now Prophase II. Attach a photo to this lab or in the space below. 23) Prophase II:

Line your chromosomes up along the “Metaphase Plate” in each cell. This is now Metaphase II. Note that since your chromosomes are no longer paired as sets, there is no independent assortment or crossing over, and Meiosis II looks like Mitosis with half the number of starting chromosomes. Attach a photo to this lab or in the space below. 24) Metaphase II:

Pull each chromosome apart and toward the appropriate pole, splitting the 2 duplicated molecules of DNA. This is now Anaphase II. Attach a photo to this lab or in the space below. 25) Anaphase II:

Draw the nucleus around each set of chromosomes, finishing Telophase II with 2 large cells, each with 2 nuclei in them. Each nuclei now has 3 chromosomes (unduplicated DNA now). Attach a photo to this lab or in the space below. 26) Telophase II:

Now you will finish Telophase II with cytokinesis and the division of the cytoplasm so that you now have 4 cells, each with 1 nuclei. Attach a photo to this lab or in the space below. 27) End of Telophase II:

Questions about Meiosis: 28) List 3 differences between mitosis and meiosis. 1. Mitosis is asexual reproduction, while meiosis is sexual one. 2. Mitosis occurs for growing and repairing cells, while meiosis happens as genetic diversity using sexual reproductive structures. 3. Mitosis occurs in all cells, while meiosis only in reproductive cells.

29) Explain the critical events during meiosis that increase genetic variation. The critical events that increase genetic variation are crossing over and mutations during this cross overs. During the process of crossing over two chromosomes of one homologous pair exchange segments, that are equal, with each other, causing mutations. 30) When you started the meiosis process, how many chromosomes were in each cell? How many chromosomes were in each cell at the end of Meiosis II? In the beginning of the process there were 6 chromosomes with duplicated DNA, and in the end of meiosis there were three unduplicated chromosomes in each cell. 31) If humans have 46 chromosomes in our body cells, how many chromosomes do we have in our testes and ovarian cells prior to meiosis? What about after meiosis? Prior to meiosis there are 23 chromosomes in each testes and ovarian cell. After the meiosis there are still 23 chromosomes. 32) When does the cell’s DNA duplicate for meiosis? Does this differ from mitosis? Usually cell’s DNA duplicates in interphase, i.e. before the process of both mitosis and meiosis. 33) How many egg and sperm are made after meiosis occurs to one cell? Hint: Review your notes before answering this question. The answer is not the same for eggs and sperm. 1 ovarian cell makes ___1__ eggs.

1 testicular cell makes ___4__ sperm. 34) How is variation created in the sex cells? Why is this important for evolution? Explain. That variation is created with the process of meiosis by crossing over and mutations. The importance of this variation in sex cells is that by the end of the process of meiosis it produces genetic diversity, and it, in turn, makes populations to better survive any environmental changes. 35) What is non-disjunction? How does it explain conditions such as Down Syndrome? Hint: You must research on the internet what non-disjunction is to answer the questions. The answer is not in your lecture notes. Nondisjunction is when one or more pairs of homologous chromosomes or sister chromatids are unable to separate normally during division which leads to the abnormal distribution of chromosomes. Down Syndrome is the disease that is caused by that abnormal division of chromosomes, i.e. when there are not two but three copies of chromosome 21.

Part IV: Karyotypes

Chromosomes are the condensed forms of our DNA. You can think of chromosomes as DNA packages that allow the DNA to fit into the nucleus of the cell (if you were to unwind DNA from just one cell it would reach over 3 feet long). Normally, humans have 46 chromosomes in each cell or 23 homologous pairs. We can visualize the chromosomes with microscopes during cell division (or mitosis). At this point chromosomes are at their most condensed form. Karyotypes use cells that are undergoing mitosis. Once the cells are collected, the chromosomes are attached to a slide and stained with Giemsa dye. This dye gives a striped appearance to chromosomes by staining regions of the DNA rich in A and T nitrogen bases. Using karyotypes, specialists can diagnose or predict genetic disorders by examining the chromosomes. Some chromosomal abnormalities include the incorrect numbers of certain homologous pairs or maybe the insertion or deletion of sections of chromosomes. Chromosomes are arranged and numbered from largest to smallest and then they are examined for any abnormalities. Today we are going to finish 3 karyotypes and try to diagnosis the abnormalities that are found. 

Go to http://www.biology.arizona.edu/human_bio/activities/karyotyping/karyotyping2.html

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You will see 3 patient histories. You will be completing karyotypes for each of these patients. Click on the link for Patient A after reading the patient history.

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In the upper left hand corner of the page you will see a chromosome that you will need to match with its homologous pair. You match the pairs by clicking on the blue link under the numbered chromosome that you think is the match.

36) After you complete each karyotype read your result page to answer the questions below.

Patient A: Number of chromosomes – 47 Sexually male or female? – female Diagnosis – Down Syndrome

Patient B: Number of chromosomes – 47 Sexually male or female? – male Diagnosis – Klinefelter's Syndrome

Patient C: Number of chromosomes – 47 Sexually male or female? – male Diagnosis – Trisomy 13 Syndrome...