1. Section 8-3 Meiosis

2. Obj 9: List and describe the phases of meiosis Meiosis I: Preceded by copying of DNA in interphase

3. Prophase I Homologous chromosomes pair  each pair = tetrad (4 chromatids)  Crossing-over may occur Chromatids twist around each other & parts are exchanged (genetic recombination)

5. Metaphase I tetrads line up

6. Anaphase I chromosomes move to opposite poles  independent assortment - random separation of chromosomes, resulting in genetic variation

7. Independent assortment http://10.20.0.2/videos/pmp/videos/wm /1MB/8VH0457G_1Mb.wmv http://10.20.0.2/videos/pmp/videos/wm /1MB/8VH0457G_1Mb.wmv

8. Telophase I chromosomes reach opposite poles cytokinesis forms 2 cells

9. Meiosis II Not preceded by copying of DNA Occurs in both cells Same 4 phases - prophase II, metaphase II, etc.

10. Meiosis II Difference: In anaphase II, chromatids separate (not chromosomes)

11. Obj 10: Compare the products of mitosis with those of meiosis Both from a 2n parent cell: Mitosis produces 2 diploid (2n) daughter cells Meiosis produces 4 haploid (1n) gametes

12. Meiosis

13. Obj 11: Explain crossing-over and how it contributes to the production of unique individuals During pairing up, chromosomes exchange DNA  results in new (unique) genetic combinations

14. Obj 12: Summarize the major characteristics of spermatogenesis and oogenesis Spermatogenesis: Cytoplasm divides evenly and produces 4 haploid cells Spermatids grow flagella and are oval

15. Oogenesis: Cytoplasm divides unevenly  Egg receives majority of cytoplasm  Polar bodies receive little cytoplasm will die and are absorbed