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Unit 8 - Meiosis

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Unit 8 - Meiosis

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  1. From Egg to Embryo – This photograph shows the After the egg [shown in orange] is released from the ovary, it travels into the fallopian tube. It stays there until a single sperm [shown in blue] fertilizes it. This unit will explain the process of meiosis in the production of eggs and sperm; summary color is blue and vocabulary words are underlined. Unit 8 - Meiosis

  2. What is meiosis?Textbook Reference pg. 265 • Meiosis is the process by which the number of chromosomes is reduced by half forming gametes EX sperm or eggs. • Two cell divisions • Meiosis animation http://www.wereyouwondering.com/wp ontent/uploads/2008/06/meiosisimagecreditnih.jpg

  3. Meiosis vs Mitosis Textbook Reference pg. 263 Mitosis creates diploid cells. Diploid, 2n = a cell with 2 of each chromosome; EX somatic [body] cells like skin cells or heart cells are diploid. • Meiosis creates haploid cells; remember, you get half your DNA from each of your parents. • Haploid, n = a cell with only 1 copy of each chromosome; EX sex cells are haploid. "Normal meiosis and nondisjunction." Genetics. Ed. Richard Robinson. New York: Macmillan Reference USA, 2010. Science in Context. Web. 3 Dec. 2013.

  4. Knowledge Check How do the sketches to the right visually represent a diploid versus a haploid cell? Which is made by mitosis versus which is made by meiosis? Turn and talk to your neighbor. http://www.personal.psu.edu/staff/d/r/drs18/bisciImages/haploidDiploid.png

  5. Meiosis I Textbook Reference pg. 266-268 • The stages of meiosis I are identical tothestages of cell cycle and mitosis; there are only slight differences during prophase. • After going through the steps of Meiosis I • Interphase 1 • Prophase 1 [+ crossing over] • Metaphase 1 • Anaphase 1 • Telophase 1 • Cytokinesis • Forms2 diploid daughter cells. • …the cell divides again! [AKA Meiosis II] "Meiosis." Biology. Ed. Richard Robinson. New York: Macmillan Reference USA, 2010.Science in Context. Web. 3 Dec. 2013.

  6. Homologous Chromosomes Textbook Reference pg. 264 • Homologs are paired Xsomes with genes of the same trait in the same order; within each pair, one chromosome comes from each parent. • Homologous chromosomes are only found in a diploid cell. "Result of Crossing Over." Genetics. Ed. Richard Robinson. New York: Macmillan Reference USA, 2010. Science in Context. Web. 3 Dec. 2013.

  7. Homologs in a Karyotype This a karyotype, a tool that geneticists use to look for mutations. It groups the homologous chromosomes in pairs; the longest pair is #1, the shortest pair is #22. http://www.biotechnologyonline.gov.au/images/contentpages/karyotype.jpg

  8. What is crossing over? Textbook Reference pg. 266 • DuringProphase I, the homologous chromosomes mix genetic material [crossing over]. • This is used to create new combinations of genes – when the cell is split in two, the geneticmaterial is now different than the parent cell due to crossing over. • Allows for more variety within organisms. • Crossing Over Animation

  9. Knowledge Check How do the sketches to the right visually represent crossing over. Turn and talk to your neighbor.

  10. Meiosis II Textbook Reference pg. 269 • After meiosis I the cell divides again! • This stage is different yet again, because the genetic material is NOTcopied during Meiosis II. • The stages are identical (interphase, prophase, metaphase, etc), butcells formed have half (haploid) of the number of Xsomes in the parent cells. • Forms 4 haploid daughter cells. • Meiosis Animation http://rationalwiki.org/w/images/thumb/b/b4/Meiosis.gif/250px-Meiosis.gif

  11. Exit Ticket (Not a Turn and Talk) Name & Period at the Top What are the similarities and differences between the processes of mitosis and meiosis? List your answer in bullet points on your sticky note. "Mitosis and meiosis." World of Anatomy and Physiology. Gale, 2010. Science in Context. Web. 4 Dec. 2013.

  12. Visualizing the Process • Take a look at pg. 267, 270, and 361 in your textbook to view the diagram of meiosis. • Use the play dough and the chalk to show meiosis at your tables. • Our organism only has 2 chromosomes; use two colors [do not completely mix them]. • Show the following: • Meiosis 1 Stages + Meiosis 2 Stages + Cytokinesis • Crossing over • Label the following: • Diploid cell • Haploid cell

  13. Nondisjunction & Polyploid Cells Textbook Reference pg. 271-273 • During meiosis, if homologous chromosomes fail to separate correctly during anaphase, then gametes have either extraXsomesor they are missing chromosomes. • This is known as nondisjunction. • Thesemutationsare passed on during fertilization [see image to the right]. • Offspring with more than the usual # of Xsomesare called polyploids. • Rare in animals, sometimes causes death. • Common in plants; polypoids are often healthier.

  14. Example of Polyploidy One of the most common examples of polyploidy in humans is Trisomy 21 [extra copy of chromosome 21]. These individuals have Down syndrome. http://www.geneticsofpregnancy.com/images/Down_syndrome.jpg http://static3.wikia.nocookie.net/__cb20120608112249/glee/images/9/98/Becky_Jackson.png

  15. Knowledge Check How do the sketches to the right visual compare normal meiosis versus nondisjunction. Turn and talk to your neighbor. "Normal meiosis and nondisjunction." Genetics. Ed. Richard Robinson. New York: Macmillan Reference USA, 2010. Science in Context. Web. 3 Dec. 2013.

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