1. Meiosis Division of Sex Cells

2. Meiosis  A process of reduction division in which the number of chromosomes per cell is cut in half through the separation of homologous chromosomes in a diploid cell.  Diploid – 2 sets of chromosomes  Haploid – 1 set of chromosomes  Homologous – chromosomes that each have a corresponding chromosome from the opposite sex parent

3. Meiosis

4. Meiosis Stages  Meiosis usually involves 2 distinct stages  Meiosis I  Meiosis II

5. Prophase I  Each chromosome pairs with its corresponding homologous chromosome to form a tetrad.  There are 4 chromosomes in a tetrad.  The pairing of homologous chromosomes is the key to understanding meiosis.  Crossing-over may occur here  Crossing-over is when chromosomes overlap and exchange portions of their chromatids.

6. Prophase I

7. Metaphase I  Spindle fibers attach to the chromosomes

8. Metaphase I

9. Anaphase I  The fibers pull the homologous chromosomes toward opposite ends of the cell.

10. Anaphase I

11. Telophase I & Cytokinesis  Nuclear membranes form.  The cell separates into 2 cells.

12. Telophase I

13. Prophase II  Meiosis I results in two haploid (N) cells.  Each cell has half the number of chromosomes as the original cell.

14. Prophase II

15. Metaphase II  The chromosomes line up similar to metaphase in mitosis.

16. Metaphase II

17. Anaphase II  Sister chromatids separate and move to opposite ends of the cell.

18. Anaphase II

19. Telophase II  Meiosis II results in 4 haploid cells.

20. Telophase II

21. Gamete Formation  In males, meiosis results in 4 sperm cells  In females, meiosis results in 1 egg cell and three polar bodies, which are not used in reproduction.

22. Mitosis vs Meiosis MitosisMeiosis Results in 2 Diploid Cells (2N) 4 Haploid Cells (N) Cells are Genetically Identical Genetically Different Occurs in Somatic (Body) Cells Sex Cells