Mitosis and Meiosis

During today's class, we continued using the PRO microscope to observe either an onion root cell or an animal cell (whitefish). We need to find the different phases of mitosis when looking at these cells. For our group, we observed the onion root cell:

Interphase

Late Anaphase

Metaphase

Prophase

Telophase

After the lab, we had a lecture about mitosis and meiosis.

What's mitosis:
Mitosis produces two daughter cells that are identical to the parent cell. If the parent cell is haploid (N), then the daughter cells will be haploid. If the parent cell is diploid, the daughter cells will also be diploid.
N → N
2N → 2N
This type of cell division allows multicellular organisms to grow and repair damaged tissue.

The phases of Mitosis:

• Interphase (G1 and G2): Chromosomes are not easily visible because they are uncoiled
• G1 Interphase: The chromosomes have one chromatid.
• G2 Interphase: The chromosomes are replicated. Each one has two sister chromatids.
• Prophase: The chromosomes begin to coil. The spindle apparatus begins to form as centrosomes move apart.
• Metaphase: The chromosomes become aligned on a plane.
• Anaphase: The chromatids separate (The number of chromosomes doubles).
• Telophase: The nuclear membrane reappears. The chromosomes uncoil. The spindle apparatus breaks down. The cell divides into two.

What's Meiosis:

Meiosis produces daughter cells that have one half the number of chromosomes as the parent cell.
2N → N
Meiosis enables organisms to reproduce sexually. Gametes (sperm and eggs) are haploid.
Meiosis involves two divisions producing a total of four daughter cells.


The Phases of Meiosis: 

A cell undergoing meiosis will divide two times; the first division is meiosis 1 and the second is meiosis 2. The phases have the same names as those of mitosis. A number indicates the division number (1st or 2nd):
meiosis 1: prophase 1, metaphase 1, anaphase 1, and telophase 1
meiosis 2: prophase 2, metaphase 2, anaphase 2, and telophase 2
In the first meiotic division, the number of cells is doubled but the number of chromosomes is not. This results in 1/2 as many chromosomes per cell.
The second meiotic division is like mitosis; the number of chromosomes does not get reduced.

• Prophase I: Homologous chromosomes pair up and form tetrad
• Anaphase I: Spindle fibers move homologous chromosomes to opposite sides
• Telophase II: Nuclear membrane reforms, cytoplasm divides, 4 daughter cells formed
• Metaphase II: Chromosomes line up along equator, not in homologous pairs
• Prophase II: Crossing-over occurs
• Anaphase II: Chromatids separate
• Telophase I: Cytoplasm divides, 2 daughter cells are formed
• Metaphase I: Homologs line up alone equator

On the other hand, how could we control the system? Checkpoint is the master. Checkpoint stops the cell from going into the next phase. It stops the cell that it only allows the cell to live in a normal life style (nondividing).