Gentics

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Gentics

  1. 1. Sources of Genetic Variability in Sexually Reproducing Organisms
  2. 2. What produces genetic variety in groups of organisms that reproduce sexually? <ul><li>The chromosomes independently line up and come together during Metaphase I. This is called Independent Assortment. </li></ul><ul><li>(The positioning of each homologous chromosome at Metaphase I is totally a matter of chance. Tetrads are assembled randomly AND the orientation of one tetrad does not impact the orientation of another tetrad.) </li></ul>
  3. 4. <ul><li>Crossing over between homologous chromosomes during prophase I. </li></ul><ul><li>This occurs when portions of non-sister chromatids trade places. </li></ul>
  4. 5. <ul><li>Random fertilization of an egg by a sperm. </li></ul><ul><li>Let’s consider the following image… </li></ul>
  5. 6. 2n = ? How many possible gamete combinations could meiosis possibly make from the cell?
  6. 7. These are the possible gametes…
  7. 16. How do you calculate this? Is there a mathematical formula? <ul><li>Yes!! </li></ul><ul><li>It is - number of possible gametes = 2 n </li></ul><ul><li>If 2n = 6; n = 3 </li></ul><ul><li>That would be 2 3 = 8 </li></ul><ul><li>How many different children could be made? </li></ul><ul><li>8 possible ‘sperm cells’ </li></ul><ul><li>x 8 possible ‘egg cells’ </li></ul><ul><li>64 possible genetically different children offspring </li></ul><ul><li>So, how many different gamete varieties is it possible for your body to make?... </li></ul>
  8. 17. <ul><li>2n = 46 so n = … </li></ul><ul><li>n = 23 so 2 23 = … </li></ul><ul><li>8,388,608 (million) – that’s just the number of different gametes your body could make using meiosis… </li></ul><ul><li>8,388,608 (million) – that’s for your mate </li></ul><ul><li>You are 1 in 70,368,744,180,000 (trillion). That’s the number of genetically different children you and your spouse could make… </li></ul><ul><li>without crossing over… </li></ul>
  9. 18. How many people have lived on earth since the beginning of time? <ul><li>It is estimated that since Adam and Eve… </li></ul><ul><li>110,000,000,000 (billion) people have lived on planet earth… </li></ul><ul><li>Why has sexual reproduction never produced your clone? (unless you’re an identical twin) </li></ul><ul><li>You are 1 in 70,368,744,180,000 (trillion). </li></ul>
  10. 19. <ul><li>You REALLY are one of a kind!! Your creator made you unique!! </li></ul>

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