Lab 7 - Cell Division: Mitosis and Meiosis


How do eukaryotic cells divide to produce genetically identical cells or to produce gametes with half the normal DNA?

Pre-Lab Questions:

1. A zygote turns into trillions of cells through the processes of interphase, mitosis, and cytokinesis. These processes replicate DNA, split chromosomes, pinch the nucleus, and produce two new cells from one. It would take many mitosis divisions to produce 100 trillion cells.

2. Cell division, in bacteria, and archaea, is binary fission. This process helps theses organisms because it is how they asexually reproduce and pass on their genes.

3. CDK must work together with cyclins to ensure that the cell is ready to perform mitosis in order for the process to be carried out successfully.

4. The genetic information of, for instance, my muscle cells differ from my blood cells in that they are longer and more expanded to form the shape of a muscle.

5. Asexual reproduction for plants can be advantageous in that the process is less complex, which therefore, decreases the chances of a mistake being made during the process.

6. DNA must be replicated before mitosis occurs because the genetic information of the two new cells must be already present before the new cells are actually made, or else only one cell would have genetic information and the other would not.

7. Chromosomes go to the center of the cell to be split during mitosis, and when they are split, they move back throughout their cells.

8. The cell cycle is controlled by the multiple checkpoints in the process, that make sure everything is going smoothly in the process.

Cell division is controlled by CDKs, which, when paired with cyclins, cause the cell of an organism to move through the different stages of the cell cycle when it is ready to move on. These stages are interphase, mitosis, and cytokinesis. There are also many checkpoints throughout the process of the cell cycle that checks if the cell has completed all of the tasks necessary for survival of the two new cells.

A eukaryotic cell divides to produce new cells by first, replicating its DNA. Then, all of the chromosomes move to the outside of the cell. Next, spindle fibers from the kinetochores attach to the chromosomes and the chromosomes are pulled into the center of the cell, where they line up in the middle. Half of each chromosome is then split by the shortening of the spindle fibers as the chromosomes that will make up the two cells move away from each other. The chromosomes on both sides de-condense. Two new nuclei are formed and the cell membrane pinches in the middle, slowly forming two new cells. The new cells are genetically identical because they carry duplicates of the same exact DNA.

Part 1: Modeling Mitosis

If a cell's chromosomes are duplicated, the amount of genetic information is still the same because it is still the same DNA, with the same exact genetic information. The amount of genetic information is not increased, even though DNA was duplicated because new genetic information and codon sequences were not made.

The significance of the fact that chromosomes condense before they are moved is that without doing so, the process of mitosis would take much longer because the chromosomes would be long strands that would not be able to be split because they would not be in the correct shape. They would be unable to undergo mitosis.

The sister chromatids are separated from each other by the shortening of spindle fibers that are connected to the kinetochores that are on the poles of the cell.

If the sister chromatids failed to separate, then they would be unable to continue the process of mitosis, because for mitosis to work, sister chromatids must be separated in order to give DNA to both of the new cells being produced from the parent cell.

Part 2: Effects of Environment on Mitosis

Experimental Hypothesis: Fungal pathogen lectin increases the number of cells undergoing mitosis.

Null Hypothesis: Fungal pathogen lectin does not in any way increase the number of cells undergoing mitosis.

By using onion bulbs, I would place three in three separate containers. One container would have no lectin. The other two would have lectin in it but only a little in one container and a lot in the other.

I would measure the amount of cells that have just been introduced in each onion bulb. I would do this by using a microscope and counting them.

An appropriate control for the experiment would be no lectin at all.

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