1. Meiosis and Sexual Reproduction

2. Sexual Reproduction Diploid Cell
A cell that has chromosomes located in similar pairs.
These cells are called body cells.
In humans, body cells have 23 pairs of chromosomes (46 total chromosomes).

3. Sexual Reproduction Haploid Cell Chromosomes are not located in pairs.
Only have half of the number of chromosomes as a body cell.
These cells are called sex cells.
In humans, sex cells have 23 chromosomes.

4. Sexual Reproduction Fertilization
Occurs when a sperm cell joins with an egg cell to create a zygote.
The sperm and egg cells are haploid cells.
The resulting zygote is diploid.

5. Meiosis and Sex Cells Meiosis
Process that divides one diploid cell into four haploid cells.
Broken into Meiosis I and Meiosis II.

6. Meiosis and Sex Cells Why is meiosis important?
Ensures that sex cells are only haploid so that when they are joined they form a diploid zygote.

7. Meiosis I
Prophase I
Chromosomes copied before meiosis begins are visible as two chromatids.
Each chromatid pair links with its similar set of chromatids to form a tetrad.

8. Meiosis I
Prophase I

9. Meiosis I
Metaphase I
Chromosome pairs line up in the center of the cell.
The centromere of each pair becomes attached to one spindle fiber.

10. Meiosis I
Metaphase I

11. Meiosis I
Anaphase I
Each half of the tetrad moves to the opposite side of the cell.

12. Meiosis I
Anaphase I

13. Meiosis I
Telophase I
Cytoplasm divides to form 2 new cells.

14. Meiosis I
Telophase I

15. Meiosis II
Prophase II
Spindle fibers reappear in each of the new cells.

16. Meiosis II
Prophase II

17. Meiosis II Metaphase II
Duplicated chromosomes move to the center of the cell.
Each centromere is attached to two spindle fibers.

18. Meiosis II
Metaphase II

19. Meiosis II
Anaphase II
Centromere divides and each chromatid moves to the opposite side of the cell.

20. Meiosis II
Anaphase II

21. Meiosis II Telophase II Spindle fibers disappear.
Nuclear membrane reappears.
Cytoplasm divides at the end of meiosis.

22. Meiosis II
Telophase II

23. Summary of Meiosis Meiosis - Briefly Meiosis I Meiosis II
Starts with one diploid cell
Forms two cells
Meiosis II
Each of the two cells formed in meiosis I forms two cells
End result is four haploid sex cells

24. Mistakes in Meiosis Possible mistakes:
Haploid cells may end up with too few or too many chromosomes.
Zygotes formed from these cells may die or have deformations.