Cells, the building blocks of the human body, contain genetic information (DNA) that is passed on from parent cell to daughter cell through the cell reproduction process called cell division. When a cell divides the genetic information contained in DNA copies itself and transmits to a daughter cell through a series of processes. There are two types of cells: eukaryotic and prokaryotic and these two cell types reproduce or divide in two main ways, either Mitosis or Meiosis. Cell division can also be broken down into two reproductive categories: asexual (Mitosis) and sexual (Meiosis). (Solomon et al 2002).
Every cell contains DNA, which is in fact the vital information (genetic code) needed to construct and maneuver a human body. DNA is structured into units called genes. An eukaryotic cell nucleus contains a lot of DNA and protein that get together to form a chromosome. Therefore, the chromosome is the major carrier of genetic information. All species have different numbers of chromosomes and different types of genetic codes inside these chromosomes. Human beings usually have 46 different chromosomes; other species can have as little as 2 chromosomes or as many as 200. Most species contain between 10 and 50 chromosomes. (Solomon et al 2002).
When cells reach maturity, they must either stop growing and remain as they are, or divide and reproduce themselves. Some cells like the nerve and muscle cells in the human body don’t divide but stay the same as they reach maturity, this makes them rarer and more finite. Other cells divide when they reach maturity through the Mitosis or Meiosis types of cell division. The cells that do divide do so in what is called the cell cycle, the cycle of a cell life from one division to the next. A cell cycle from one division to the next is also called a generation as it is with human beings from one set of parents to the children. (Solomon et al 2002).
Most cells both eukaryotic and prokaryotic divide through the Mitosis processes which is asexual. An example of this might be eukaryotic human skin cells and or prokaryotic bacteria; they replicate themselves exactly but not sexually. Eukaryotic cells are different that the prokaryotic cells however because they contain much more DNA and their reproduction process is more complicated. Eukaryotic cells also reproduce sexually through Meiosis in more developed (higher on the evolutionary scale) plants and animals. During, the sexual type of cell division called Meiosis special cells called gametes (eggs and sperm) come together to create a finished product called a zygote (fetus). (Solomon et al 2002).
The main differences between Meiosis and Mitosis is that one is a form of replication without sexual contact and the other is a blending of chromosomes through the sexual process. When a cell divides by Mitosis, it makes an exact copy of its DNA and transfers this to a daughter cell, sort of like cloning. There are individual steps during the process of Mitosis called interphase, prophase, metaphase, anaphase and telophase. It is asexual reproduction where the parent cell clones itself or makes a copy of itself in the daughter cell. Meiosis, however is a different process of replication where two sex cells that are called gametes come together to form a zygote. In meiosis, there are two cell divisions, Meiosis I and Meiosis II. During the first cell division, the same stages occur that occur in Mitosis, but the new cells have half of the amount of DNA needed by a cell. The cell does a second division soon after the first, which divides the number of chromosomes in the cell in half. When a cell has half the number of chromosomes it is called a haploid cell. Haploid means half the regular number and diploid is the opposite meaning two halves. Normal cells are considered to be diploid cells and the merging of the haploid cells, thus sexual reproduction, creates them. (Solomon et al 2002).
The individual steps in the process of Mitosis are called interphase, prophase, metaphase, anaphase and telophase. Interphase is the normal condition of a cell where it grows and collects materials and sort of hangs out waiting to change. After interphase, when the cell reaches a certain point, it readies itself for prophase. During prophase, a cell gets the idea that it\'s time to divide and it prepares to duplicate its DNA making centinoles. Then comes metaphase, where all the pieces called centinoles arrange in a line. DNA is lined up along a central axis and the centinoles send out tubules that connect to the DNA that is condensed into chromosomes, then strands of a chromosome are connected at the center with something called a centromere. Metaphase is the phase when it is easiest to see and photograph cells. Anaphase is where division actually begins, half of the chromosomes are pulled to one side of the cell, and half go the other side. When the chromosomes reach the side of the cell, it\'s time to move on to Telophase. Telophase is the final stage of cell division where the cell membrane closes in and splits the cell into two pieces. Presto, You have two separate cells each with half of the original DNA. Then back to interphase where the process starts all over again. (Solomon et al 2002).
Meiosis is similar to Mitosis because the cells go through the same stages of interphase, prophase, metaphase, anaphase and telophase. However, during Meiosis, the cell divides itself a second time shortly after the first. Interphase II is pretty much the same, but in prophase II, the DNA starts to become concentrated and chromosomes are formed. Each pair of chromosomes has a centromere. The centinoles begin their journey to opposite sides of the cell in metaphase II and pairs of chromosomes are lined up at the center of the cell and then pulled to each side. Meiosis is different because there is something called crossing over that happens with the DNA, crossing over is an exchange of genes. The genes are mixed up and like shuffled around, not a precise duplicate like mitosis. The cell divides, leaving two new cells with a mixture of chromosomes in each. Then anaphase II chromosomes are split and pulled to opposite sides of the cell. Each one is split in two pieces, they don\'t divide up the DNA between the new cells; they split the DNA that exists. Each daughter cell will get one half of the DNA needed to make a functioning cell. Finally, during Telophase II DNA is completely pulled to the sides and the cell, begins to squeeze together. When all is said and done, you are left with four haploid cells that called gametes. Gametes will eventually combine with other gametes to form a zygote. (Solomon et al 2002).
So, you can see that the two types of cell division and or reproduction are indeed similar. Mitosis and Meiosis do use the same processes, however, the results vary considerably. The main difference is that in mitosis there is asexual cloning resulting in exact chromosome duplication and in Meiosis the is a blending of the chromosomes of the parent cells to create new daughter cells that have different chromosomes that the original. Hopefully, this is an adequate and comprehensible description of cell division. (Solomon et al 2002).
Solomon, Eldra P., Linda R. Berg, and Diana Martin. 2002. Biology, 5/e. Saunders College Publishing/ Philadelphia PA.
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