1. Mitosis and Meiosis

2. The Role of Mitosis Two Stages -Divide nucleus & DNA
-Divide cell (cytokinesis)
Purpose: to produce 2 identical cells for…
-Growth
-Repair of tissue
-Replace dead cells
-Asexual Reproduction

3. Terms to know! DIPLOID (2n): Full complement of chromosomes.
In humans 2n = 46
HAPLOID (n): Number of unique chromosomes
In humans n = 23

4. Diploid or Haploid? In a cabbage cell the Diploid number is 2n = 18
What is the Haploid number?
n = 9
How many homologous pairs? 9

5. The Cell Cycle
Most of the cell’s time is spent in Interphase!

6. Stages of Mitosis - Interphase
This is the parent cell
Rapid growth
Cell doing its job
DNA replication (chromatin)
Prepares for division

7. Stages of Mitosis - Prophase
DNA condenses into chromatids (thicker)
Nuclear membrane disappears
Spindle fibers form from centrioles and attach to centromeres.

8. Stages of Mitosis - Metaphase
Chromatids line up down the middle.
Pulled into place by spindle fibres.

9. Stages of Mitosis - Anaphase
Chromatids are pulled apart (by spindle fibers)

10. Stages of Mitosis - Telophase
Nuclear membrane reforms
Cytokinesis occurs (cell divides)
2 identical daughter cells (DIPLOID – 2n)

11. Mitosis in Plant Cells No centrioles A cell plate forms,
then cell wall.

12. Meiosis and Variation
Variation is key for species survival, allows organisms to adapt!
During Meiosis, two events occur which increase variation…

13. Independent (Random) Assortment
When tetrads line up at Metaphase I, the paternal and maternal chromosomes line up randomly on the left and right.
223 = different combinations!

14. Crossing Over
While the dyads are in the tetrad, pieces of homologous chromatids can change places, creating different chromosomes.
This is desirable and occurs frequently
If one piece gets misplaced, a mutation occurs (genes are missing)

15. Stages of Meiosis
Use your textbook (Pg ) and the handout to document the steps in Meiosis