1. Sexual Reproduction & Meiosis

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

3. 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

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

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

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

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

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

9. 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

10. 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)

12. Diploid (2n)

13. Haploid (n)