1. Question of the Day 1.Where do humans do meiosis? 2.Why do humans do meiosis? 1.In the testicles and ovaries 2.To ensure genetic variation

2. Fig. 13-8 Prophase I Metaphase I Anaphase I Telophase I and Cytokinesis Prophase II Metaphase IIAnaphase II Telophase II and Cytokinesis Centrosome (with centriole pair) Sister chromatids Chiasmata Spindle Homologous chromosomes Fragments of nuclear envelope Centromere (with kinetochore) Metaphase plate Microtubule attached to kinetochore Sister chromatids remain attached Homologous chromosomes separate Cleavage furrow Sister chromatids separate Haploid daughter cells forming

3. Metaphase I Fig. 13-8a Prophase IAnaphase I Telophase I and Cytokinesis Centrosome (with centriole pair) Sister chromatids Chiasmata Spindle Homologous chromosomes Fragments of nuclear envelope Centromere (with kinetochore) Metaphase plate Microtubule attached to kinetochore Sister chromatids remain attached Homologous chromosomes separate Cleavage furrow

4. Fig. 13-8b Prophase IMetaphase I Spindle apparatus Sister chromatids Chiasmata Spindle Genetically different chromatids Metaphase plate Tetrad with Crossing over Fragments of nuclear envelope Spindle Fiber attached to kinetochore

5. Fig. 13-8c Anaphase I Telophase I and Cytokinesis Sister chromatids remain attached Homologous chromosomes separate Cleavage furrow

6. Fig. 13-8d Prophase II Metaphase II Anaphase II Telophase II and Cytokinesis Sister chromatids separate Haploid daughter cells forming

7. Fig. 13-8e Prophase IIMetaphase II New spindle fibers form Sister chromatids positioned on metaphase plate

8. Fig. 13-8f Anaphase II Telephase II and Cytokinesis Sister chromatids separate Haploid daughter cells forming

9. Fig. 13-8 Prophase I Metaphase I Anaphase I Telophase I and Cytokinesis Prophase II Metaphase IIAnaphase II Telophase II and Cytokinesis Centrosome (with centriole pair) Sister chromatids Chiasmata Spindle Homologous chromosomes Fragments of nuclear envelope Centromere (with kinetochore) Metaphase plate Microtubule attached to kinetochore Sister chromatids remain attached Homologous chromosomes separate Cleavage furrow Sister chromatids separate Haploid daughter cells forming

11. Fig. 13-9a MITOSIS MEIOSIS MEIOSIS I Prophase I Chromosome replication Chromosome replication 2n = 6 Parent cell Prophase Metaphase Metaphase I Anaphase I Telophase I MEIOSIS II Daughter cells of meiosis II n n n n 2n2n 2n2n Daughter cells of mitosis Anaphase Telophase

12. Fig. 13-9b SUMMARY MeiosisMitosis Property DNA replication Number of divisions Occurs during interphase before mitosis begins One, including prophase, metaphase, anaphase, and telophase Genetic variation Does not occur Number of daughter cells Two, each diploid (2n) and genetically identical to the parent cell Role in the animal body Enables multicellular adult to arise from zygote; produces cells for growth, repair, and, in some species, asexual reproduction Occurs during interphase before meiosis I begins Two, each including prophase, metaphase, anaphase, and telophase Occurs during prophase I along with crossing over between nonsister chromatids; resulting chiasmata hold pairs together due to sister chromatid cohesion Four, each haploid (n), containing half as many Chromosomes as the parent cell; genetically different from the parent cell and from each other Produces gametes; reduces number of chromosomes by half and introduces genetic variability among the gametes