Cell Biology Meiosis and Mitosis

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Cell Biology (CP8121)
Experiment 2: Observing Mitosis and Meiosis on cell specimens (Formal report)

Name: Wong Chung An
Class: DMLS/FT/1B/02
Admin number: P1138687

This experiment aims to observe mitosis and meiosis on cell specimens. It involves the modelling of the stages of meiosis and also the staining procedures to identify mitosis in onion root tip. There are two parts to the procedure of the experiment whereby the first is staining and observing mitosis in onion root tips and the second being observing and comparing mitosis between whitefish blastula and onion root tip. The results are that the five stages of mitosis have been observed and sketched, together with a comparison of telophase in plant and animal cells. The difference between the two types of cell division mitosis and meiosis has also been recorded. The conclusion is that all the objectives of the experiment have been met and it is recommended that the mitotic spindle be stained for a more complete picture of the various stages of mitosis.

1) Introduction
It is important that the experiment is carried out so as to differentiate between the two types of nuclear division, mitosis and meiosis. Mitosis is a process mainly for the growth and replacement of somatic cells and it involves the replication of chromosomes which results in having two daughter cells each same as the parent nucleus. On the contrary, meiosis is for the production of gametes which is essential for an organism’s reproduction and it comprises of two successive nuclear divisions which results in the production of four haploid cells.

Mitosis: A process which replicates chromosomes exactly so that each of the daughter cells contains identical information. The process of mitosis involves five stages. The five stages are: Interphase, Prophase, Metaphase, Anaphase and Telophase respectively.

Meiosis: A process whereby two successive nuclear divisions will produce four haploid cells. There are two rounds of cell division in meiosis, mainly meiosis I and meiosis II. Meiosis I is identical to that of mitosis whereas meiosis II is a round of reductional division. The process of meiosis has allowed for an escalation of genetic variations because of the crossing over of the genes. This process is crucial as it produces half the number of chromosomes as per the human sex cells. For humans, every gamete contains 23 chromosomes and fertilisation of an egg by a sperm will restitute the diploid number of 46 chromosomes

2) Objectives
* Learn a staining procedure to identify mitosis using onion root tip. * Compare and contrast mitosis in plants and animals.
* Compare and contrast stages of mitosis and meiosis
* Model stages of meiosis.

3) Procedures

(a) Preparation and observation of onion root tip slide

1) An onion root tip was obtained and the first 1-3mm of its root tip was cut off using a scalpel. The root tip was then placed at the centre of a clean slide using a forceps.

2) Then, the root tip was covered with 2-3 drops of 1N HCL solution and then placed over the hot plate for 3-5 seconds using a slide holder.

3) Without touching the root tip, the excess acid was then blotted off using a paper towel.

4) After which, the root tip was then covered once again, this time in 3-4 drops of 0.5% Toluidine Blue solution.

5) The excess stain was blotted off and a cover slip was added.

6) To spread out the stained root tip for visualisation, the slide was placed in the middle of a folded paper towel and applied pressure upon by placing the thumb directly above the cover slip and having it gently pressed on against a lab bench.

7) The slide was examined on low power on the microscope and embryonic cells which are square-like were looked for.

8) Once the mitotic figures were found, the microscope was switched to a higher power.

9) The phases that were seen were sketched on the datasheet....
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