2. II. Sexual Reproduction & Meiosis By Addy Lundberg John Swett High School Crockett, CA

3. A. Sexual Reproduction 1. Asexual repro. needs only one parent 2. Sexual repro. needs two sex cells –a. Sperm--male sex cell –b. Egg--female sex cell

4. B. Importance of Sex Cells 1. In body cells, chromosomes found in pairs –a. Pairs form because chromosomes are alike –b. Cell with 2 of every kind of chromosome is diploid –c. Sex cell is haploid--23 in egg or sperm

5. B. Importance of Sex Cells 2. Sexual repro starts with cex cell & ends with fertilization –a. Zygote is formed--in human now is diploid or 2n with 46 chromosomes

6. C. Meiosis--Sex Cell Formation 1. In meiosis, there are 2 divisions of the nucleus: meiosis I & meiosis II 2. Prophase I: double stranded c’somes and spindle fibers appear; nuclear membrane and nucleolus fade

7. 3. Metaphase I: chromosome pairs (chromatids) line up –spindle fibers attach to centromeres and centrioles 4. Anaphase I: chromotids separate from matching pair

8. 5. Telophase I: cytoplasm divides and 2 cells form

9. 6. Prophase II: chromatids and spindle fibers reappear

10. 7. Metaphase II: chromatids line up in the center of the cell –spindle fibers attach to centromere & centriole 8. Anaphase II: centromere divides –chromosomes split and move to opposite poles

11. 9. Telophase II: spindle fibers disappear –nuclear membrane forms around chromosomes at each end of cell –each nucleus has half the # of chromosomes as the original (haploid) –now there are 4 sex cells (daughter cells)

13. Diploid (2n)

14. Haploid (n)