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Investigation into the varies stages of mitosis

Extracts from this document...

Introduction

Investigation into the varies stages of mitosis In my practical assessment I was observing nuclear division, mitosis and the stages involved in the process. Although in reality the process is continuous it has been divided into four stage called Prophase, metaphase, anaphase, telophase. Mitosis is the used for the replacement of cells and repair of tissues. It is also the basis of asexual reproduction. Prophase which is said to be the first stage of nuclear division or mitosis, is the stage where the centriole replicates just before hand and the chromosomes have started to coil up becoming shorter and thicker; they become more visible and stain more intensely. This is all in the early stages. In late prophase the centrioles move to opposite ends or poles of the nucleus, the nuclear envelope 'disappears' or it breaks up into small vesicles not visible by a light microscope. The nucleolus also disappears it forms parts of several chromosomes. Then at the end of prophase a spindle is formed. In metaphase each centriole reaches a pole they help to organise production of the spindle microtubules. The chromosomes line up along the equator of the spindle; they are attached by their centromeres to the spindle, which is made from protein microtubules. Each chromosome then splits at the centromere and is pulled apart then in the next phase, anaphase the chromotids (two identical sister chromatids make one chromosome) move to opposite poles, centromeres first, pulled by the microtubules. In the last suggested stage the nucleolus begins reforming as well as the nuclear envelope. The chromatids have reached the poles of the spindle; they will now uncoil again to form chromatin. Each chromatid contains one DNA molecule, which will replicate itself during interphase before the next division (interphase is another part of the cell cycle). Remains of the spindle are starting to break down, cytokinesis starts to take place this is division of the cytoplasm and cell into two by constriction from the edges of the cell. ...read more.

Middle

than those for other stages, therefore it could be that the prophase stage is longer because more things happen within the cell in the stage which has been classed as prophase in mitosis. In this information taken from the source shown late prophase is named as an almost separate stage prometaphase, it shows how much activity goes on in the cell in the stage of mitosis named prophase 1. Prophase * The two centrosomes of the cell, each with its pair of centrioles, move to opposite "poles" of the cell. * The mitotic spindle forms. This is an array of microtubules, synthesized from tubulin monomers in the cytoplasm, that develops from each centrosome. * The chromosomes become shorter and more compact. . Prometaphase * The nuclear envelope disintegrates. * A protein structure, the kinetochore, appears at the centromere of each chromatid. * With the breakdown of the nuclear envelope, spindle fibers attach to the kinetochores as well as to the arms of the chromosomes. The microtubules attached to a kinetochore exert tension on its chromatid. For each dyad, one of the kinetochores is attached to one pole, the second (or sister) chromatid to the opposite pole. Failure of a kinetochore to become attached to a spindle fibers interrupts the process. 3. Metaphase The tension is proportional to length; thus if a dyad approaches one pole, the tension in the opposite direction increases and the dyad is pulled back to an equilibrium position midway between the poles. In due course, all the dyads reach this position, the equatorial plane or metaphase plate. The chromosomes are at their most compact at this time. 4. Anaphase The sister kinetochores suddenly separate and each move to its respective pole dragging its attached chromatid (chromosome) behind it. Separation of the sister chromatids depends on the breakdown of the cohesins that have been holding them together. It works like this. ...read more.

Conclusion

My own results were found the most accurate way I thought possible. I made sure the same cells were not counted by using the microscope needle and a piece of paper to examine the next section of the slide I had not yet looked at by putting paper over the slide I had not yet looked at and counting abut 5 rows of cells, as the cells were arranged in fairly accurate rows. I am fairly sure I did not count the same cells more than once and my method was fairly accurate. However I do not know how others conducted their investigations and how they ensured reliability of their results. This puts a question mark over reliability of the overall results and also effects accuracy. The results should be fairly reliable as I have analysed results from 16 samples. The individual results do have a wide range varying from 3 up to 14 in the anaphase stage. This however as already stated could be due to individual differences (each slide contains different individual cells which gives rise to variation). Reliability could be improved by repeated investigation of the same slide then the error due misidentification or other errors can be judged and taken into consideration. Also each person doing the investigation should take the same steps to improve reliability e.g. How to ensure cells are not counted more than once. Perhaps when each cell is observed there should be a second check person if more than one person agrees that the cell is that particular stage of mitosis it is more likely to be correct. There is argument to suggest that my conclusion, that each stage of mitosis is not equal is fairly safe. However, there is also a lot of evidence to suggest that it is not very reliable i.e. I can only account for the reliability of my own results. To say my conclusion was completely safe I would have to do further investigational work taking the steps suggested to improve reliability. Linda Stevenson Mitosis ...read more.

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