Mitosis v Meiosis: The history of Down syndrome from historical origins until modern times

Subject: Health Care
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The history of genetics is traceable into major process within the body of the organism, namely Mitosis and Meiosis. The process of progression from mitosis to meiosis underlines the whole genetic transfer mechanism from organisms to their offspring (Cregan, 2007). Mitosis refers to the cell division process through which the chromosomes of the cell is replicated and then separated into two nuclei, which are then added the necessary body cell components such as the cell membranes, the cell organelles and the cytoplasm, to emerge as two different cells, which are not genetically identical (Clift & Schuh, 2013). On the other hand, Meiosis is a cell division process that entails the reduction of the cell chromosome number by half, after which each half is then replicated to form four component nuclei of new cells, which are genetically identical (Courtois, Schuh, Ellenberg & Hiiragi, 2012). In this respect, the major difference between Mitosis and Meiosis is that; while Mitosis is the cell division method that is involved in the multiplication of the non-gamete cells in the body to give rise to asexual reproduction, Meiosis is the process through which the gamete cells are multiplied, to give rise to sexual reproduction (Cregan, 2007). Nevertheless, the whole process of formation of new offspring from their parent organisms must entail both the Mitosis and Meiosis cell division processes, except for the single cell organisms, whose multiplication and reproduction is purely a mitotic process (Lavania, Lavania & Vimala, 2002). Therefore, through the cell division process known as the cell cycle, the process of creating new cells both for the non-gamete and the gamete cells occur.

The process of cell division occurs as a 4-step process, which starts in the cell chromosomes, representing the part of a DNA molecule of an organism, which carries the heredity information of the organism transferable from the parent organism to the offspring. Chromosomes are made up of chromatins, consisting of both the DNA and another structural material known as the histones, and then packaged in the nucleus of a cell (Cregan, 2007).The DNA is packaged as a protein strand that in the nucleus of a cell, and it varies in both structure and appearance, based on the different stages of the cell cycle (Lavania, Lavania & Vimala, 2002). Therefore, in order for the human cells of a parent to replicate and give rise to the body cells that forms a human offspring, the process of cell division starts in the cell chromosomes through the process of mitosis. The chromosomes are condensed within nucleus of the cell and then the DNA strand is copied, so that the initial DNA strand is replicated into two identical copies of DNA (Clift & Schuh, 2013). Each of the replicated DNA is then attached to the structural material histones to form two identical chromatids, which are a replica of one another, to emerge with what is referred to as the daughter chromosomes (Cregan, 2007). Once the two daughter chromosome are formed within the nucleus of the cell, the process of separating the nucleus into two equal parts, each with a single daughter chromosome, then starts.

The process of separation of the occurs where the daughter chromosomes are first aligned towards the middle of the cell nucleus, so that the splitting of the cell is achieved in a balanced manner that will produce two equal parts of the cell nucleus, each carrying a daughter chromosome (Courtois, Schuh, Ellenberg & Hiiragi, 2012). The aligning of the daughter chromosomes to the center of the nucleus is followed increase in bulk of the cell cytoplasm to form new organelles, which will be subdivided into forming the new cell organelles  component (Lavania, Lavania & Vimala, 2002). The daughter chromosomes are then pushed towards the edge of the cell in opposite directions together with their organelle components, after which the nucleus then separates and is embodied by the cell membrane to create two new cells (Cregan, 2007).

On the other hand, Meiosis occurs in the gamete cells of the humans, which consists of the sperm and the egg cells (Cregan, 2007). The process of meiosis is however different from that of mitosis, in that as opposed to producing two identical and replica crones of cell chromosomes, meiosis first halves the number of chromosomes in the nucleus of a cell to produce two non-identical chromosomes, which are then divided by a similar cell division as that of mitosis to produce four new cells from the initial one gamete cell (Clift & Schuh, 2013). In this respect, the human cell, which comprises of 46 chromosomes is first halved into two new cell components each with 23 chromosomes in meiosis I, which are then undertaken through the second stage of meiosis II that is similar to mitosis, to form two different cells that are now identical from each of the initially halved cell, to create a total of four new cells, each with 23 chromosomes (Cregan, 2007).This process is the basis of sexual reproduction in humans, allowing for the combination of the chromosomes in the sperm cell with the chromosomes in the egg cells to form a normal human cell offspring with 46 chromosomes, which are them multiplied through the process of mitosis cell division, to generate the necessary body cells for the growth of the fetus into full grown human being (Courtois, Schuh, Ellenberg & Hiiragi, 2012).

Nevertheless, it is this process of the halving the initial body cell with 46 chromosomes into two component cell with 23 chromosomes each that is very critical for genetically healthy human progression of the humans from parents to their offspring. This s because, during the meiosis I stage where the body cell is first halved to form two daughter cells each with 23 chromosomes; an error may arise, resulting in one of the daughter chromosome carrying more component chromosomes than the other, such that one of the daughter chromosomes will have an extra chromosome, while the other is in shortage (Cregan, 2007). The outcome of this error is that the erratic or discordant chromosomes that are produced either with extra chromosomes or with a shortage of chromosomes is then transmitted from parent to their offspring during the fertilization of the egg by the sperm, to form an offspring with either a shortage or an excess of component.

Therefore, the cell division process, especially during meiosis state I is very critical and the defining moment for the rise of the discordant chromosome, which gives rise to the genetic disorder diseases (Hernandez & Fisher 1996). The genetic disorder trisomy 21, commonly known as Down’s syndrome, is caused by an error in meiosis stage I, where the halving of the human cell is accidentally erratic, resulting in the two daughter chromosomes emanating from the process having unequal chromosome, with one of the halved daughter chromosomal cell having an extra pair of chromosome 21, while the other halved daughter completely lacks this chromosome (Baatout, 1999). Thus, once the fertilization of an egg consisting of an extra chromosome 21 by a normal sperm occurs, the outcome is an offspring with 46 chromosomes, one of which has an extra chromosome 21 (Cregan, 2007). Therefore, instead of the offspring having the normal two of chromosome 21, the offspring now has 3 chromosome 21s. The cell normal cell division of the offspring through mitosis is then continues to multiply cells that have 3 chromosome 21s, resulting in the genetic disorder known as Down Syndrome, or trisomy 21, to indicate that the chromosome 21 in the offspring are three, as opposed to the normal two (Baatout, 1999). Therefore, the history of Down syndrome dates back to an initial error in meiosis stage I for a certain human, which has been transmitted over to generations of offspring over the course of the human history through mitosis, to the current state of Down syndrome in modern times.

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  1. Baatout, S. (1999). Molecular basis to understand polypoloidy. Hermatology and Cell Therapy 41(4), 169-7.
  2. Clift, D., & Schuh, M. (2013). Restarting life: fertilization and the transition from meiosis to mitosis. Nature Reviews Molecular Cell Biology, 14(9), 549-562.
  3. Courtois, A., Schuh, M., Ellenberg, J. & Hiiragi, T. (2012). The transition from meiotic to mitotic spindle assembly is gradual during early mammalian development. Journal of Cell Biology 198(3): 357.
  4. Cregan, E. R. C. (2007). All About Mitosis and Meiosis: Life Science. Huntington Beach: Teacher Created Materials Pub.
  5. Hernandez, D. & Fisher E.C. (1996). Down syndrome genetics: unraveling a multifactorial disorder. Hum. mol. Genet.,5, 1411-1416.
  6. Lavania, U. C., Lavania, S. & Vimala, Y. (2002). Mitosis–meiosis transition, the regulation of the means to sexual reproduction. CURRENT SCIENCE, 82(1), 15-16.
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