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Mitosis and Meiosis, the defining differences.

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Introduction

Mitosis and Meiosis, the defining differences. The cell theory was first proposed by Schleiden in 1838 and Schwann in 1839. This theory was then extended upon by Rudolf Virchow in 1855 declaring that new cells only came from pre-existing cells. Shortly after, in 1887, Weismann suggested a specialist form of division occurred in the manufacture of gametes. These two forms of division are called Mitosis and Meiosis respectively. By definition, Mitosis and Meiosis are very similar, both being methods of cell division. However, the way in which the daughter cell is produced in these processes vary. The biological differences in these two processes lie between Mitosis and Meiosis I, as Meiosis II is almost identical to Mitosis. Mitosis As a consequence of Mitosis, a parent nuclei divides into two daughter nuclei, each with the same number of chromosomes as the parent nucleus. The division of the whole cell follows this. In order to accomplish this chromosome firstly replicate themselves during interphase. The two replicate chromosomes are known as chromatids and separate during mitosis. Cell division is a continuous process with no sharp distinction between the phases. There are 3 main stages: Interphase: this is the episode of synthesis and growth. The cell produces many materials essential for its own growth and for carrying out all its functions. ...read more.

Middle

Finally it is important for asexual reproduction, as the offspring are identical to the parent. Meiosis Meiosis is a form of nuclear division in which the chromosome number is halved from the diploid number, to the haploid number. As a result of Meiosis four daughter cells are formed from one parent cell. Each daughter cell has half the number of chromosomes of the parent cell. Meiosis occurs during the formation of sperm and egg cells, therefore is essential for sexual reproduction. Like Mitosis, Meiosis is a continuous process and is conveniently divided into the prophase, metaphase, anaphase and telephase. However, this cycle is repeated twice to produce the four daughter cells. I will be detailing Meiosis I, as Meiosis II is almost identical to Mitosis. Prophase I: The chromosomes contract and are seen to have divided into two chromatids. As in Mitosis, the chromosomes coil, causing them to shorten and become thicker. One of the key characteristics of prophase I of Meiosis is that the paternal and maternal chromosomes come together in homologous pairs. This pairing is called synapsis. Each homologous pair is called a bivalent, and so consisting of four strands. The points of exchange of chromatid material are called chiasmata, and the swapping of materials is referred to 'crossing over.' This is the longest and most complicated phase in Meiosis. ...read more.

Conclusion

Somatic cells are referred to as diploid (2n) whereas gametes are haploids (n), thus explaining that Mitosis produces 2 cells where Meiosis produces 4. During prophase, differences arise. For example, in mitosis, the homologous chromosomes remain separate whist they pair up in meiosis. In metaphase of mitosis, the chromosomes line up singly, however in metaphase I of Meiosis, bivalents align on the metaphase plate. The 2 double chromosomes are called a tetrad when they are lined up side by side. Crossing over occurs during the formation of the tetrad, resulting in the formation of chiasmata. Anaphase accommodates the centromeres to divide during Mitosis, whereas they remain whole in Meiosis. The arrangement of chromosomes also differs between the two processes. Daughter cells of Mitosis have 2 sets of chromosomes, and are genetically identical to the parent cell. Meiosis daughter cells have only one member of each pair of chromosomes, and only half the genes from the parent cell. This stage occurs in the telephase. Crossing over and random separation of homologous pairs of chromosomes allows genetic diversity. The occurrence of these cells also differs. Where mitosis cells occur in haploid, diploid or polyploid cells, during the formation of somatic cells, Meiosis only occurs in diploid or polyploid cells, during the formation of gametes and spores. Mitosis and Meiosis are both immensely important in life, meiosis for creating it, and mitosis for maintaining it. ...read more.

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Here's what a teacher thought of this essay

4 star(s)

This is a well researched report that covers most of the necessary aspects of mitosis and meiosis.
!. The structure is good but at least one subheading is missing.
2. There is some information that is alluded to but not included, such as the second stages of meiosis.
3. The information sources need to be referenced.
4. The use of language and key terms is outstanding.
****

Marked by teacher Luke Smithen 23/07/2013

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