Observing Mitosis

Chromosome pairs line up across the equator of the spindle at metaphase I (5). In anaphase I the chromosomes separate and travel to opposite ends of the spindle. The chromosomes migrate to the equators of two new spindles for metaphase 2 (7). Next the chromatids are pulled apart in anaphase 2 to form four clusters of chromosomes in telophase 2. The nuclear envelopes reform around four haploid nuclei that will give rise gamete

Exercise 3A is a study of mitosis. You will simulate the stages of mitosis by using chromosome models.You will use prepared slides of onion root tips to study plant mitosis and to calculate the relative duration of the phases of mitosis in the meristem of root tissue. Prepared slides of the whitefish blastula will be used to study mitosis in animal cells and to compare animal mitosis and plant mitosis.

In this experiment first the stages of an onion cell undergoing mitosis are going to be observed and every stage is going to be detected and drawn on paper. A brief description to what is going on should be attached to the pictures. This is important to understand the basics of cell division which is necessary growth,repair and asexual reproduction. Second the number of cells undergoing each phase is going to be counted to figure out in which phase the cell remains the most. If interphase is the stage in which the cell grows and prepares for cell division then the

Purpose: The purpose of this lab was to calculate the amount of time that was spent by a cell in each of the phases of mitosis. Also, it is used to be able to compare the process of mitosis between plant and animal cells.

These bivalents line up along the equator during metaphase I, the arrangement of the bivalent is completely random and relative to the orientation of the other bivalents, this is known as the independent assortment of chromosomes. This is followed by anaphase I where the homologous chromosomes separate and move to the opposite poles of the cell. At telophase I the cell divides into two, each cell contains one chromosome from each homologous pair. The second stage of meiosis is similar to mitosis.

A) Meiosis consists of two cell divisions and is broken up into Meiosis I and Meiosis II. At the beginning of the Cell Cycle, in this case there are four chromatids each from the homologous pairs being A, a, B, b. This is the Diploid number (4) meaning it is 2 times the haploid number that will be seen at the end of meiosis II. During the S phase of interphase, the chromatids replicate and reach the end of G2 phase. Now starting meiosis, during the first stage of prophase I the chromosomes condense and pair up through synapsis with their sister chromatids creating AA, aa, BB, bb. After they pair up they go through a process called crossing over, where the homologous chromosomes share a piece of their genetic material with each other. Crossing over allows for the genetic diversity of chromosomes. Now there are four homologous chromosomes Aa, Aa, Bb, Bb, each containing heterozygous alleles because the sister chromatids exchanged genetic information with their homologous pair. During late prophase I, spindle fibers being to form where they will later attach to a homologous chromosomes centromere. The next stage is Metaphase I. During metaphase I, the homologous pairs line up at the metaphase plate, also known to be the center of the cell. The homologous pairs form a tetrad which is considered a group of four homologous chromosomes. These homologous chromosomes orient themselves randomly, which is know as the process of independent

Table 1: Record your data for the number of cells in each stage of the cell cycle observed in normal tissues.

Without cell division and the cell cycle nearly all life would fail to exist. Cell division allows an organism to not only replace its own cells but to create offspring. The cell cycle consists of two main parts: interphase and mitotic phase. Within these two phases the processes can be broken down into further categories. Interphase can be broken down into three subphases that are the necessary preparations the cell makes in order to be ready to divide during mitosis. For this lab we looked mainly at the mitotic phase because of its fascinating and rapid changes to the cell. The cell types we looked at were prepared slides of whitefish and onion root tip.

They may have poor eye sight, the cells may not have transferred on to the slide properly, the microscope may have malfunctioned,

[A labelled diagram of the end of the Prophase stage of a cell here would be

To observe mitosis in onion root tip cells and record the different phases of mitosis.

In this lab experiment, there were three objectives we analyzed and experimented in identifying mitosis cells. The three objectives we were observing were mitosis in animal cell, plant cell, and staining chromosomes in dividing cells. First off, my partner and I removed two inch-ling roots and placed it in the prepared 3 ml of methanol-acetic acid fixative solution in a small vial. We began with this first step because the roots need to be fixed for 15 minutes at 60oC in an incubator. We made two sample, in case we made an error.

Plants are organisms that can reproduce sexually through meiosis and create more cells through mitosis (Russell et al. 2013). For studying mitosis, the common onion is an ideal choice. Because it is easy for onions to germinate without soil, it is easy to control any substances provided to the plant. The onion root tips are only a few cells thick and grow quickly making them ideal for time efficiency. The onion root tip needs to be squashed between the cover slip and the microscope in order to reduce the slide preparation’s total depth. To dye condensed chromosomes, such as those undergoing mitosis, a stain is used to make

Making the onion tip root cell slide was successful. Our results supported the hypothesis because we saw cells in the onion root tip in prophase, metaphase, and anaphase. As we went up in power objectives, each phase of the cell became more definitive. The cell root was a great indicator of the structures of the different cycles of the cell. This is important because we will be prepared for future labs working with the microscopes and can now adjust it for the best view of the slide. We practiced working with the compound light microscopes and different phases of the cell cycle. Onion root tips are useful to observe mitosis because the cells are frequently diving as the root grows. So when we stained the cell, we caught many cells in different phases. The significance of this lab was to better understand the process and stages of mitosis and meiosis and compare and contrast the mitotic process in plants and animals. We grasped the concepts of what the chromosomes look like, and what they look like in each step of the processes. Having read much about mitosis and meiosis, seeing these cells was the real application of describing and understanding the stages.

The main focus of this lab was to be able to understand the different phases of mitosis and the cell cycle and also identify what those stages may look like. Mitosis is the process in which concerns the production of new cells. For example, when apoptosis(cell death) the process of Mitosis begins to replace the dead cells. To be able to familiarize ourselves with this concept, we took a sample of an onion root and had it put through a process to be able to look at the different phases under the microscope. We found that the majority of the cells were mostly undergoing Interphase or Prophase which are the phases in charge of crossing over of DNA and where the chromosomes then become visible and the nuclear envelope dissipates. The conclusion of this lab was that Mitosis is essential for the production of new cells. In the case of the onion root sample, the cells were damaged leading to the tester to undergo Mitotic cell division and it was found that mainly Interphase and Prophase were the stages that occurred in this lab.