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Transcript
Columbia College Biology 110 Laboratory Manual LABORATORY EXERCISE 3 – MITOSIS AND MEIOSIS Objective: 1) To understand the principles behind mitosis and meiosis. 1) Mitosis The following materials are available to help you understand the process of mitosis. You do not need to go through all of them, but use as many of the materials as is necessary to help you understand the process. - Photographic microslides – booklets numbered 53 and 55 - Demonstration slides Study the demonstration showing the various phases of mitosis under the microscope. Do not move the slide as this changes the position of the section under focus for the next person. Use the fine adjustment only if you need to get a sharper focus. Make note specifically of various characteristics of each phase, as you need to be able to recognize each one. Take the slides labeled onion root tip (Allium) and whitefish or Ascaris and locate the various phases of mitosis under the compound microscope. Q1. What is the purpose of mitosis? Q2. Draw the following stages of mitosis (early interphase, late interphase, prophase, metaphase, anaphase and telophase) in the space below in a cell whose diploid number is 8. Each chromosome should be easily distinguished and each diagram should be adequately labeled. Q3. What events in mitosis ensure that each daughter cell gets an identical set of chromosomes? Q4. What would happen if arbitrary separation of chromosomes occurred during mitosis? 2) Meiosis The following materials are also available to help you understand the process of meiosis. You do not need to go through all of them, but use as many of the materials as is necessary to help you understand the process. - Photographic microslides – booklet numbered 92 - Demonstration slides Study the demonstration showing the various phases of meiosis under the microscope. Do not move the slide as this changes the position of the section under focus for the next person. Use the fine adjustment only if you need to get a sharper focus. Make note specifically of various characteristics of each phase. Take the slides labeled Lillium anther and grasshopper testis and locate the various phases of meiosis under the compound microscope. Q5. What is the purpose of meiosis? Q6. If a diploid parent cell has 50 chromosomes (2n = 50), answer the following two questions for each of the cell types below: 1) the number of chromosomes 2) the number of DNA molecules a) A cell at prophase of mitosis? b) A cell at prophase I of meiosis? c) A cell at anaphase of mitosis? d) A cell at anaphase I of meiosis? e) A cell at prophase II of meiosis? f) A cell at anaphase II of meiosis? Q7. Referring to the same cell from the previous question, how many homologous pairs of chromosomes would there be in the following cell types: a) A cell at prophase of mitosis? b) A cell at prophase I of meiosis? c) A cell at prophase II of meiosis? d) A cell at anaphase of mitosis? e) A cell at anaphase II of meiosis? Q8. How many genetically different cells can possibly be formed (not including crossing over) when a diploid cell with 44 chromosomes undergoes meiosis? Q9. Explain how it is possible for a human cell to have 44 autosomes and XXY sex chromosomes. Q10. If 2N = 8, show how chromosomes align at the metaphase plate: a) During mitosis. b) During the first division of meiosis. c) During the second division of meiosis. d) Explain, using diagrams, how many genetically different daughter cells are possible in a cell with 2N = 8 undergoing meiosis.