Mitosis & Meiosis Lab

Introduction: This lab explores the process of Mitosis and Meiosis. The experiments intend to help us get a good grasp on the different stages of the processes, the difference between the two, as well as the results of each process and what these results mean.

3A.1 - Observing Mitosis in Plant Cells Using Prepared Slides of an Onion Root Tip

Purpose: Under a microscope, we will view an onion root tip. This allows us to observe dividing plant cells, they will be in different stages of mitosis. It will help us learn to distinguish the different stages of mitosis so we can recognize them easily.

Procedure & Methods:

1. Examine prepared slide of onion root tip
2. Locate the meristematic region of the onion with the 10X objective lens
3. Use the 40X lens to study individual cells
4. Using the descriptions provided, identify and take pictures of cells in different stages of the mitotic cell cycle

Data:

3A.2 - Time for Cell Replication

Purpose:

Viewing an onion root tip under a microscope, we will see the different stages of mitosis in plant cells. The number of cells found in each of the stages will be recorded. by doing this, we will be able to find out at which stage a cell spends most of its time.

Procedure & Methods:

1. Observe every cell in a high-power field of view and determine which phase of the cell cycle it  is in.This is best done in pairs. The partner observing the slide calls out the phase of each cell while the other partner records. Then switch so the recorder becomes the observer and vice versa. Count at least two full fields of view. If you have not counted at least 200 cells, then count a third field of view.

*This is best done in pairs, with one person viewing the cells and calling it out to their partner who can record the data

2. Record data in Table 3.1
3. Calculate the percentage of cells in each phase, and record this in Table 3.1

Data:

Analysis & Conclusion (for 3A.1 and 3A.2):

The purpose of part A was to identify and count the number of cells in every phase in order to determine the time spent in each. In our data, most of the cells we observed were found in the interphase stage of mitosis, for 37.97% of it’s life cycle. This is fairly accurate when compared to the ideal percentage of time spent in this phase (34% of it’s life cycle) demonstrated in the “Onion Root Tip Cell Cycle” pie chart below. However, the percent of time spent in telophase that we observed in our experiment is remarkably higher than the ideal percentage. We calculated that, for 27.85% of the cell’s life, it was in telophase while we should have observed only around 17% of cells in this phase of mitosis. We believe that, when observing the cells, we mistakenly recorded cells that were in prophase or anaphase as being in telophase. Perhaps our error was a result of the image not being clear enough to be able to distinguish between the phases properly. Our data should have looked more like this:

vasanapbiolab.weebly.com/mitosis.html

This shows us the correct percentage of a cell’s life that should be spent in each stage of mitosis. Notice how this ideal percentage of time spent prophase and anaphase is considerably higher than those collected in our data.  

3B.1 - Stimulation of Meiosis

3B.2 - Time for Cell Replication

Purpose:

In this experiment we will use the ascomycete fungus, Sordaria fimicola, to demonstrate the results of crossing over during meiosis.

Procedure & Methods:

1. Obtain two images of hybrid Sordaria asci containing both tan and black ascospores.
2. Carefully tally up the amount of 4:4 asci (this means that they are not crossing over) and enter it in the second column of Table 3.3
3. Count the amount of asci showing crossover and record it in the third column of Table 3.3
4. Add up the number of 4:4 asci and asci showing crossover to get the total number of asci. Enter this into Table 3.3.Take the total number of asci showing crossover and divide it by the total number of asci. Then divide that by 2, and multiply it by 100 to calculate map units (gene to centromere distance).

Sample 1

Sample 2

Data:

Sample 1

Sample 2

Analysis & Conclusion:

We learned from this experiment that the further a gene is to the centromere, the more likely it is to cross over. This is illustrated in our data; the second sordaria has greater crossing over and gene to centromere distance than the first sordaria. Logically, this makes sense because the further out a gene is located on a chromatid, the more likely it is to get exchanged with other chromosomal material as the ends of chromatids cross over.