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Class Topics

Hand in the W.S. Science skills before the bell rings 2A hand in p. 157 #16 and #18 Chapter 7 Quiz 1 Continue Chapter 7 Genetic variation Gametogenesis “I would rather fail in a cause that someday will triumph, than to win in a cause that I know will someday fail.” Woodrow Wilson.

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Class Topics

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  1. Hand in the W.S. Science skills before the bell rings 2A hand in p. 157 #16 and #18 Chapter 7 Quiz 1 Continue Chapter 7 Genetic variation Gametogenesis “I would rather fail in a cause that someday will triumph, than to win in a cause that I know will someday fail.” Woodrow Wilson To review learning about genetic variation due to meiosis and about gametogenesis Title: Biology 1/17/07 Class Topics Objectives: Friday, December 20, 201912:27 PM

  2. Class Assignments What By When • Chapter 7 Quiz 1 1/17/07 • W.S. Science Skills 1/17/07 • 2A only – paragraphs from p. 157 (16 & 18) 1/17/07 • Meiosis W.S. 1/19/07 • Chapter 7 Test 1/23/07 • Due this class period • Due next class period • Due in the future

  3. Grade Sheet

  4. Postquiz Activities • Reread 144-149 • Review • Independent assortment • Crossing over • Random mating

  5. Genetic variation • Allows for new genetic combinations • Unlike mitosis • 1. Independent assortment • Random distribution of homologous chromosomes • Each of the 23 pairs segregates independently • 223 combinations (8,388,608) from one cell

  6. Genetic variation (cont.) • 2. Crossing-over • Occurs during Prophase I when homologous chromosomes synapse • Trading of genetic material between homologous chromosomes (switching genes) • Increases genetic diversity

  7. Genetic variation (cont.) • 3. Random fertilization • Random fertilization means each gamete was independently assorted • (223 * 223) = 70,368,744,177,664 combinations

  8. Importance of genetic variation • Very important for evolution • change in characteristics of a population from one generation to the next • The pace of evolution can be sped up by increased genetic variation • Depends on natural selection

  9. Crossing Over • Video Clips • Items to note • Another name for crossing over? • In mitosis? • Why or why not? • How often? • Large chromosomes • Small chromosomes • What if crossing over doesn’t occur?

  10. Homologous chromosomes somatic cells gametes 1 division tetrads cytokinesis chromatids Synapsis unpaired chromosomes diploid cells crossing over 2 divisions haploid cells ovum Venn Diagram

  11. Meiosis and Gamete Formation • Spermatogenesis • Formation of sperm in the testes • Primary spermatocytes (2n) • Secondary spermatocytes (n) • Spermatids (n) • Sperm (n) • 4 haploid cells from one germ cell

  12. Oogenesis • Primary Oocyte (2n) • Secondary Ooctye, Polar Body (n) • 1 Ootid, Polar bodies (n) • 1 Ovum (n)

  13. Sperm size - small moves by flagellum millions made per day no food produced in testes Ovum size - very large no movement fixed number all made by 3rd month of development Yolk (amnion) supplies food Ovaries Sperm vs Ovum

  14. Meiosis W.S. • Front side (Meiosis) • Guinea pig 2n = 64 • Back side (Meiosis & Fertilization) • do not fill in the blanks on the right (fertilization side) • Do not use 4 different colors, two will suffice • Step 1 should be metaphase I • Step 3 should be both telophase I and prophase II

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