1. Meiosis
Division of Sex Cells

2. Meiosis
A process of reduction division in which the number of chromosomes is cut in half through separation of homologous pairs in a diploid cell.
Diploid – 2 sets of chromosomes
Haploid – 1 set of chromosomes
Homologous – pairs of matching chromosomes that come from each parent

5. Meiosis

6. Meiosis Stages Meiosis involves 2 distinct cell divisions: Meiosis I
Meiosis II

7. 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 meiosis.
Crossing-over may occur here
Crossing-over is when chromosomes overlap and exchange portions of their DNA

8. Prophase I

9. Metaphase I Spindle fibers attach to the chromosomes
Homologous pairs line up side by side

10. Metaphase I

11. Anaphase I
The fibers pull the homologous chromosomes toward opposite sides.

12. Anaphase I

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

14. Telophase I

15. End of Meiosis I Meiosis I results in two haploid (N) cells.
Each cell has half the number of chromosomes as the original cell.

16. Prophase II
Chromosomes re-condense and nuclear membrane breaks down again (similar to Prophase of Mitosis)

17. Prophase II

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

19. Metaphase II

20. Anaphase II
Sister chromatids separate and move to opposite sides.

21. Anaphase II

22. Telophase II and Cytokinesis
Meiosis II results in 4 GENETICALLY DIFFERENT haploid cells. (gametes)

23. Telophase II

24. Gamete Formation
In males, meiosis results in 4 sperm cells (spermatogenesis)

25. Gamete Formation
In females, meiosis results in 1 egg cell and three polar bodies, which are not used in reproduction. (Oogenesis)

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