Sci 9 Lesson 4 April 6 - Meiosis


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Sci 9 Lesson 4 April 6 - Meiosis

  1. 1. Homework from last class: <ul><li>Complete the Introduction to Meiosis and Reproductive Systems worksheet </li></ul><ul><li>Study for your Genetics and Reproductive Systems quiz </li></ul>
  2. 2. Quiz Time! <ul><li>You have about 10 minutes to write the quiz. </li></ul><ul><li>Good luck! </li></ul>
  3. 3. Chapter 6 pp. 191-197 Ch. 6.1 Meiosis
  4. 4. Meiosis <ul><li>Meiosis: the form of cell division that produces gametes (sex cells) with half the number of chromosomes as body cells </li></ul><ul><li>Diploid (2n)  Haploid (n) </li></ul><ul><li> parent cell sex cells </li></ul><ul><li>Meiosis only occurs in gonads (testes or ovaries) </li></ul><ul><li>Male: spermatogenesis: formation of sperm (spermatozoa) </li></ul><ul><li>Female: oogenesis : formation of eggs (ova) </li></ul>
  5. 5. <ul><li>Meiosis is similar to mitosis , but there are several differences : </li></ul><ul><li>Involves 2 cell divisions </li></ul><ul><li>Results in 4 cells with ½ the genetic information </li></ul><ul><li>(n instead of 2n) </li></ul>Meiosis occurs in 2 phases: Meiosis I (1 st cell division) Meiosis II (2 nd cell division) Meiosis I Meiosis II
  6. 6. Spermatogenesis & Oogenesis Sperm formation Egg formation Meiosis I Meiosis II Spermatogenesis Oogenesis
  7. 7. <ul><li>Meiosis I </li></ul><ul><li>Prior to meiosis I, DNA replicates once , in interphase </li></ul>Fig 6.4 p. 191
  8. 8. <ul><li>Meiosis I </li></ul><ul><li>In meiosis I, a pair of matching homologous chromosomes , one from each parent, lines up at the equator </li></ul><ul><li>Homologous chromosomes: a pair of matching chromosomes </li></ul>Fig 6.5 p. 191
  9. 9. <ul><li>Meiosis I </li></ul><ul><li>Homologous chromosomes line up at the equator </li></ul><ul><li>The homologous chromosome pair separates and moves to opposite poles of the cell </li></ul><ul><li>2 daughter cells result </li></ul>Fig 6.5 p. 191
  10. 10. <ul><li>Crossing Over </li></ul><ul><li>Crossing over: event in meiosis I where non-sister chromatids exchange segments of DNA ; results in variation in gametes </li></ul><ul><li>As a result of crossing over, each chromosome picks up new genetic information from the other </li></ul>
  11. 11. <ul><li>Independent Assortment </li></ul><ul><li>Independent assortment: an event in meiosis I where homologous pairs of chromosomes separate and sort themselves into daughter cells </li></ul><ul><li>Genes are shuffled  leads to genetic diversity </li></ul>
  12. 12. <ul><li>Crossing Over and Independent Assortment </li></ul>Fig 6.6A p. 192
  13. 13. <ul><li>Meiosis II </li></ul><ul><li>DNA not replicated again before meiosis II begins </li></ul><ul><li>Meiosis II is like mitosis (in both processes, the chromatids of each chromosome are pulled to opposite poles </li></ul><ul><li>Each daughter cell inherits 1 chromatid from each chromosome </li></ul><ul><li>4 haploid (n) daughter cells result </li></ul>Fig 6.4 p. 191
  14. 14. <ul><li>Outcome of Meiosis II </li></ul>Fig 6.6B p. 193
  15. 15. <ul><li>Summary of Meiosis </li></ul>
  16. 16. <ul><li>Meiosis Animation </li></ul><ul><li> </li></ul>
  17. 17. <ul><li>Chromosome Mutation in Meiosis </li></ul><ul><li>Chromosome mutations can occur spontaneously </li></ul><ul><li>Chromosome mutations  can cause genetic changes </li></ul><ul><li>Parts of chromosomes can be inverted, deleted, duplicated or moved to another spot (see p. 194) </li></ul>Mutagens can cause chromosome mutations <ul><li>Mutagens (ex. radiation, chemicals) can cause chromosome changes </li></ul><ul><li>Can lead to genetic disease or death </li></ul>
  18. 18. <ul><li>Consequences of failed separation of chromosomes in meiosis </li></ul><ul><li>Failed separation = a gamete may end up with no chromosome or too many copies of a chromosomes . </li></ul><ul><li>Zygotes that result from these gametes rarely survive, and if they do, they will have serious genetic disorders . </li></ul>Diagnosing Genetic Disorders The chromosomes of an individual can be studied Karyotype: an image that shows the number of chromosomes a person has; used to diagnose genetic disorders Down syndrome karyotype
  19. 19. Homework for next class: <ul><li>Complete Activity 6-1D worksheet (if not completed in class) </li></ul><ul><li>Complete Check Your Understanding questions 2, 3, 5, 6, 7, 9, 10, 11, 13, 15, 16 (p. 203) </li></ul><ul><li>Read over class notes and check class blog </li></ul><ul><li> </li></ul>
  20. 20. Works Cited <ul><li>Images taken from the following sources: </li></ul><ul><li> </li></ul><ul><li> </li></ul><ul><li> </li></ul><ul><li> </li></ul><ul><li> </li></ul>