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Copy into Notes… Aim # 4: How and why does meiosis happen? Meiosis: sexual reproduction process that produces sex cells, each with half the parent’s DNA Name-NOHELYMENDEZ Date-1-9-08 Class- 805 Science- Ms. Sowin Class Work # 4 Directions: For each question, type your answers in the spaces provided. Use your notes, the websites, and the table to help you: Go to http://www.cellsalive.com/meiosis.htm 1.Write down 3 observations the meiosis interactive (3 things you see going on during meiosis) a.it is changing b.its seperating c.now there are two # of cell divisions # of cells produced # of chromosomes in each new cell Types of cells produced Functions in body Mitosis in Humans 1 2 46 Meiosis in Humans 2 4 23 All body cells except sperm and egg cells Growth, repair, maintenance Sperm and egg cells only reproduction 2. How many cell divisions take place in meiosis? 2 3. What kind of cells does meiosis produce and for what function? Sperm and egg cells only 4. How are mitosis and meiosis similar and different? They are both cell divisions Most of your growth occurs because your body added new cells. New cells are produced as old cells go through mitosis. Just before mitosis begins, the chromosomes double. Then, the chromosomes line up and eventually pull apart so the cell divides into 2 identical cells with the same exact DNA. In humans, body cells originally contain 46 chromosomes and after mitosis is complete, each new human body cell contains 46 chromosomes. Likewise, fruit flies each have eight chromosomes in their body cells and after mitosis is complete, each new fruit fly body cell has 8 chromosomes. Sexual reproduction involves another type of cell division called meiosis. Like mitosis, a cell splits in half to produce two daughter cells. Unlike mitosis, in meiosis each daughter cell divides again. As a result, a cell that undergoes meiosis can produce 4 sex cells, each with only half as many chromosomes as a normal body cell. Sperm and egg cells are produced by meiosis. When a sperm and egg join, they are able to produce a zygote that has a full set of chromosomes- half from each parent. For example, a body male’s body cell that originally has 46 chromosomes undergoes meiosis and produces a sperm cell that has 23 chromosomes (half of 46). A woman’s body cell after meiosis would produce an egg cell that has 23 chromosomes. When a man and woman reproduce together, their baby would have body cells that have 46 chromosomes (23 + 23). Similarly, fruit fly cells that originally have 8 chromosomes would only have half as many- 4 chromosomes after meiosis, but a fertilized fruit fly egg would have 8 chromosomes again. 5. A cell with 100 chromosomes undergoes mitosis. How many chromosomes are in the new body cell after mitosis is over? (a) 200 (b) 100 © 50 (d) 0 My answer to # 5 is…..200 6. Which step must occur before mitosis can begin? (a) the cell’s DNA is copied (b) The nuclear membrane breaks down © the chromosomes separate (d) the cell splits in half My answer to # 6 is letter….b 7. A cell with 40 chromosomes undergoes meiosis to produce an egg cell. How many chromosomes are in the egg cell? (a) 80 (b) 60 © 40 (d) 20 My answer to # 7 is letter…80 8. Which cells are produced by meiosis? (a) nerve cells (b) sperm cells © skin cells (d) muscle cells My answer to # 8 is letter…b 9. All cells in the human body have 46 chromosomes, except sperm and egg cells. Explain why…because the sperm eggs must separate to reach the egg so it wont have any chromosomes because the sperm egg will grow REMEMBER TO SAVE YOUR WORK, AND THEN UPLOAD IT TO YOUR WIKISPACE!!! How to UPLOAD and SAVE documents on YOUR OWN WIKISPACE! 1. 2. 3. 4. 5. 6. Make sure you save your Aim 4 Class Work Click on your class # and your name on the navigation bar on the right. Click on the edit this page tab at the top. Click on Green Tree to Insert Images and Files Browse for the Aim 2 Class Work Click Open 7. Press Upload 8. Double Click on the correct W document. 9. PRESS SAVE ON THE LOWER RIGHT SIDE OF YOUR PAGE!