1. Mitosis and the Cell Cycle
Practical Of Genetics
Lab. 2
Mitosis and the Cell Cycle

2. Purpose
To prepare slides of onion root tips demonstrating the stages of mitosis (somatic cell division) and identification of cells in the various stages of mitosis.

3. Prokaryotic cells (bacteria) reproduce asexually by binary fission.
Background
Prokaryotic cells (bacteria) reproduce asexually by binary fission.
During binary fission
The bacterial chromosome is duplicated.
The cell elongates.
The two chromosomes migrate to opposite ends of the cell.
Each daughter cell receives one chromosome and is identical to the parent cell.
Binary fission is a relatively fast and simple process.

4. Eukaryotes are diploid, which means they have two sets of chromosomes; one set of chromosomes is inherited from each parent.
There are 2 types of cell division :
Mitosis
Meiosis 

5. Interphase M phase The cell cycle G1 phase Mitosis S phase Cytokinesis
The cell division cycle is a sequence of events in a eukaryotic cell between one mitotic division and another.
Interphase
G1 phase
S phase
G2 phase
M phase
Mitosis
Cytokinesis

7. Interphase الطور التحضيري) )
- Is the phase of the cell cycle in which the cell spends the majority of its time and performs the majority of its purposes including preparation for cell division.
- Chromatin appears dispersed, DNA replication occurs.
(Chromatin is a mass of uncoiled DNA and associated proteins called histones).
- In preparation for cell division, it increases its size and makes a copy of its DNA.
Cell cycle

8. G1 ( initial growth cycle )
Interphase
G1 ( initial growth cycle )
Cellular contents ,excluding the chromosomes, are duplicated.
S ( DNA synthesis )
Each of the 46 chromosomes is duplicated by the cell.
G2 (2ndgrowth stage)
The cell checks the duplicated chromosomes for error, making any needed repairs. G0
A resting phase where the cell has left the cycle and has stopped dividing.

9. M phase
- Mitosis and cytokinesis together define the mitotic (M) phase of the cell.
- This accounts for approximately 10% of the cell cycle.

10. Mitosis ( nucleus division)
Mitosis is the first part of M-phase and divided into four distinct phases(prophase, metaphase, anaphase and telophase).

11. Mitosis Prophase - Nuclear envelope and nucleoli disappear,
- Chromatin condenses to chromosomes
- Nuclear envelope and nucleoli disappear,
- Spindle starts to form attach to the kinetochore ( a portion of the centromere ).

12. Mitosis
Metaphase
All chromosomes align in one plane at the center of the cell called the equatorial plane (also referred to as the metaphase plate).

13. Mitosis Anaphase: Spindle fibers shorten. The kinetochores separate.
The sister chromatids (daughter chromosomes) are pulled apart and begin moving to the cell poles.

14. Mitosis
Telophase:
The last stage of division, is marked by a noticeable condensation of the chromosomes, followed by
formation of a new nuclear envelope around each group of chromosomes.
The chromosomes gradually de-condense to form the chromatin seen in interphase.
The nucleoli reappear.

15. Cytokinesis (cytoplasmic division)
- Usually occurs at the end of telophase.
- In plant cells cytokinesis is accomplished by the formation of a cell plate.
- Animal cells separate by forming a cleavage furrow.

16. Interphase M phase G1 phase S phase The cell cycle G2 phase
Mitosis
Metaphase
Prophase
Telophase
Anaphase
Cytokinesis

17. Preparing An Onion Root Tip Squash:
The cells at the tip of the root are constantly dividing to allow the root to grow.
Because each cell divides independently of the others, a root tip contains cells at different stages of the cell cycle. This makes a root tip an excellent tissue to study the stages of cell division.

18. Onion bulbs have been rooted in water.
Growth of new roots is due to the production and elongation of new cells.
Mitotic divisions are usually confined to the cells near the tip of the root. Follow the procedure outlined below to make your own root tip preparation.

19. Procedure: 
1. Obtain two small cups, label one “ HCL” and the other “Carnoy.” Pour in enough of each to just cover the bottom of its cup.
2. Obtain an onion bulb that is just beginning to show the emergence of roots. Cut a small piece of root off and use forceps to place it in the cup of 1M HCL for 4 min at 60ºC. 
3. Transfer the root into the cup of carnoy fixative. The root should remain in the carnoy fixative for 4 minutes.

20. 4. After the 4 minutes, place the root on a slide
4. After the 4 minutes, place the root on a slide. Then, cut off the bottom 1 or 2mm of the root tip & discard the rest.
5.Cover the root with a 1drop of Crystal Violet for 2 minutes. After the 2 minutes, blot away the stain; be careful not to touch the root tip.
6.When the stain has been blotted away, cover the root tips with drops of water to remove the stain. Apply water drops until water runs mostly clear. Blot slide without touching root tip.
7. Gently lower a cover slip over the root tip. Cover the slide with a paper towel and with your thumb (or a pencil eraser), firmly press on the cover slip; Do not twist the cover slip. The pressure will spread the cells into a single layer.

21. 8. Then using the fingernail polish, carefully paint the edges of the cover slip. Make sure not to move the cover slip. Finally allow the slide to dry.
9. Now you are ready to view you slide under low power. Place your prepared slide on the microscope.
10. Use the low power objective on your microscope to look for thin layers of cells and then use the 40X power objective to observe mitotic stages in individual cells.

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