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Chapter 11 Sexual Reproduction and Meiosis

Chapter 11 Sexual Reproduction and Meiosis. Rev Question. When and where does meiosis occur in humans? Why is meiosis necessary? “reductive division”. What are the stages of Meiosis? Meiosis I vs Meiosis II Prophase I Metaphase I Anaphase I Telophase I. McGraw-Hill Meiosis.

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Chapter 11 Sexual Reproduction and Meiosis

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  1. Chapter 11 Sexual Reproduction and Meiosis Rev Question Meiosis and Gametes

  2. When and where does meiosis occur in humans? Why is meiosis necessary? “reductive division” Meiosis and Gametes

  3. What are the stages of Meiosis? Meiosis I vs Meiosis II Prophase I Metaphase I Anaphase I Telophase I McGraw-Hill Meiosis Meiosis unique features Meiosis and Gametes

  4. How does Prophase I differ from Prophase of Mitosis? • Bivalents form • -- “synapsis” • -- homologous chromosome pairs • 2) Crossing over occurs • -- exchange of DNA segments • -- “chiasmata” • During Metaphase 1, • bivalents are aligned at equator • not individual chromosomes Question Meiosis and Gametes

  5. During Meiosis I parental homologous chromosomes are independently sorted to daughter cells Chromosome reduction occurs during Meiosis I Interkinesis What happens during Meiosis II? Chromosome reduction ---- sister chromatids separate Gametes produced McGraw-Hill sorting Question Meiosis and Gametes

  6. Comparison of Meiosis and Mitosis Metaphase looks different for each process Question 2N=4 Question Meiosis and Gametes

  7. Homework assignment: 10 points: due next class For a cell where 2N=6, draw a series of diagrams showing the chromosomes moving through the stages of meiosis. In one of the diagram clearly label: -- a pair of homologous chromosomes -- a bivalent Label all stages Make diagrams large, clear and neat Also answer the following questions: For an organism with a chromosome number of 2n = 56: A. How many pairs of homologous chromosomes does each normal body cell possess? ___ B. How many chromosomes does each cell possess after mitosis? ____ C. How many pairs of sister chromatids are present at the beginning of meiosis? ___ D. How many bivalents will form during prophase-I? ____ E. How many chromosomes does each cell possess after meiosis? ___ Drawings must be neatly done and chromosomes drawn with adequate detail. Chromosomes, bivalents and spindle fibers must be recognizable as these structures. Meiosis and Gametes

  8. Why does meiosis in females yield only 1 viable gamete? Why does spermatogenesis in males assure 50:50 ratio of males to females? Sex of the sperm determines sex of the offspring Meiosis and Gametes

  9. How can errors during meiosis cause Congenital birth disorders? Non-disjunction of chromosomes e.g., Down’s syndrome What is karyotyping? “trisomy 21” -- an example of “aneuploidy” Many effects -- reduced intellectual development -- heart and kidney defects -- often fatal -- early onset Alzheimer's Meiosis and Gametes

  10. How does meiosis create genetic diversity? 1) crossing over 2) random assortment of chromosomes and later … 3) random pairing of gametes Meiosis and Gametes

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