1. Meiosis

2. Mitosis vs. Meiosis:

3. Mitosis vs. Meiosis: BOTH INVOLVE CELL DIVSION
Goal of Mitosis: to produce 2 daughter cells that are genetically identical to the parent (same DNA).
-Used for growth
-1 set of division
-1 diploid cell  2 diploid cells

4. Mitosis vs. Meiosis:
Goal of Meiosis: to produce sperm or eggs, also called gametes; contains ½ the genetic information as the parent.
-Used for reproduction
-2 sets of division
-1 diploid cell  4 haploid cells

5. Diploid vs. Haploid Cells:
Diploid: having 2 sets of chromosomes (2n).
Ex: human body cells have 46 chromosomes
Haploid: having one set of chromosomes, as in a sperm or egg (n).
Ex: human egg and sperm cells have 23 chromosomes.

6. Haploid & Diploid

7. Meiosis Meiosis animation:
Beginning of third class

8. In Meiosis there are 2 sets of division taking place.

9. Interphase occurs before Meiosis begins.
In Interphase, the chromosomes have not yet condensed into distinct chromosomes.

10. Interphase
The chromosomes have replicated (made a double), and prepares for division.

11. Replicated DNA
DNA is replicated along with organelles and other cellular components and the cell prepares for division.
Each half of the duplicated chromosome is called a sister chromatid.
Chromatids are connected to each other by centromeres. 

12. Meiosis - Prophase I
The chromosomes are completely condensed. In meiosis (unlike mitosis), the homologous chromosomes pair up with one another.
Crossing over occurs, in which homologous chromosomes exchange genetic material.

13. Meiosis - Metaphase I The nuclear membrane has dissolved.
Homologous pairs line up in the middle of the cell.
Spindle fibers attach to each homologous chromosome.

14. Meiosis - Anaphase I Spindle fibers shorten.
The chromosomes move to opposite ends of the cell.
Notice that these are chromosomes, not chromatids!!

15. Meiosis - Telophase I & Cytokinesis
The cell begins to divide into two daughter cells.
It is important to understand that each daughter cell can get any combination of maternal and paternal chromosomes, because of crossing over.

16. Meiosis - Prophase II The nuclear envelope begins to break down.
The spindle fiber forms.
Compare the next few steps to Mitosis!

17. Meiosis - Metaphase II
A haploid number of chromosomes line up in the middle of the cell.
Spindle fibers connect to the centromeres.
Do you remember what haploid means?

18. Meiosis - Anaphase II
The spindle fibers shorten and the sister chromatids move to opposite sides of each cell.
Looks similar to Anaphase in Mitosis.

19. Telophase II & Cytokinesis
The chromosomes reach the poles, and the nuclear membrane reforms around each nucleus.
Meiosis results in four gametes, or sex cells
Each carries half the number of chromosomes of regular body cells.

20. Is Meiosis I or Meiosis II more similar to Mitosis?
Answer: Meiosis II (the second division) is more similar to Mitosis.