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Bio 178 Lecture 22

Bio 178 Lecture 22. Meiosis. http://homepage1.nifty.com/scilla/sonota/ityou/ityou.html. Reading. Chapter 12. ?. Quiz Material. Questions on P 240 Chapter 12 Quizzes on Text Website (www.mhhe.com/raven7). Outline. Sexual Reproduction The Sexual Life Cycle Meiosis.

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Bio 178 Lecture 22

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  1. Bio 178 Lecture 22 Meiosis http://homepage1.nifty.com/scilla/sonota/ityou/ityou.html

  2. Reading • Chapter 12 ? Quiz Material • Questions on P 240 • Chapter 12 Quizzes on Text Website (www.mhhe.com/raven7)

  3. Outline • Sexual Reproduction • The Sexual Life Cycle • Meiosis

  4. The Sexual Life cycle • Alternation of Generations All sexual life cycles alternate between a haploid and diploid state. In some organisms the diploid stage is dominant and in others the haploid stage is dominant. This is a consequence of mitosis and meiosis: • Mitosis Maintains chromosome number. • Meiosis Halves chromosome number.

  5. The 3 Types of Sexual Life Cycle

  6. Unique Features of Meiosis McGraw-Hill Video

  7. Genetic Variation in the Sexual Life Cycle • Maternal and Paternal Chromosomes If there was no exchange of genetic material between the homologues  each gamete would receive an entire homologue that is either maternal or paternal. • The Process of Crossing Over Purpose Genetic Variation Synapsis Pairing of chromosomes along their length (after DNA replication). Homologues attached to nuclear envelope.

  8. Synaptonemal Complex

  9. Synaptonemal Complex (Enzymes) http://www.ucl.ac.uk/~ucbhjow/bmsi/synapto.html

  10. Spermatocyte Synaptonemal Complex Green = SCP 1 Blue = DNA Red/Yellow = Centromere Top = Normal Bottom = SCP 3 deficient http://7e.devbio.com/article.php?ch=19&id=188

  11. Genetic Variation in the Sexual Life Cycle Crossing Over • DNA is exchanged between the non-sister chromatids at the chiasmata. • Recombination nodules break and rejoin homologous chromatids. http://www.blc.arizona.edu/courses/181summer/10.html

  12. Post Crossing Over • Synaptonemal complex breaks down. • Homologues are now joined only by common centromeres and chiasmata. • Homologues released from nuclear envelope.

  13. Meiosis

  14. Comparison of Meiosis and Mitosis McGraw-Hill Video

  15. Meiosis • Cell Divisions 2 divisions after the chromosomes have replicated: Meiosis I Separation of homologous chromosomes. Meiosis II Separation of sister chromatids. • Ploidy Diploid  Haploid

  16. Meiosis I • Prophase I Chromosomes finish condensing. Synapsis and crossing over occur. Centrioles (animal cells) move to opposite poles and spindle fibers form between them. Nuclear envelope breaks down. Chiasmata move to the ends of the chromosomes ( terminal chiasmata).

  17. Prophase I

  18. Meiosis I (Cntd.) • Metaphase I Homologous chromosomes align on the metaphase plate, attached to the kinetochore microtubules. These are attached only to the outward facing kinetochores. Independent assortment - The homolgue orientation is random.

  19. Metaphase I

  20. Independent Assortment McGraw-Hill Video

  21. Meiosis I (Cntd.) • Anaphase I Homologues separate and are pulled to opposite poles. • Telophase I Homologues reach opposite poles. Nuclear envelopes may form. • Cytokinesis May occur.

  22. Anaphase I

  23. Telophase I

  24. Meiosis II There may be a brief interphase, but NO DNA SYNTHESIS occurs. • Prophase II Centrioles move to opposite poles and spindle fibers form. If the nuclear envelope reformed it breaks down. • Metaphase II Chromosomes align at the metaphase plate. Kinetochore microtubules are attached to both sides of the centromere.

  25. Prophase II

  26. Metaphase II

  27. Meiosis II (Cntd.) • Anaphase II Sister chromatids separate and are pulled apart ( chromosomes). • Telophase II Chromosomes reach opposite poles. Nuclear envelopes form. • Cytokinesis Results in 4 daughter cells.

  28. Anaphase II

  29. Telophase II

  30. ? Biodidac. http://biodidac.bio.uottawa.ca/thumbnails/filedet.htm?File_name=19-7D&File_type=GIF

  31. Sources of Genetic Variation in Meiosis • Crossing over • Independent assortment

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