Cell Division
I. What is the Cell Cycle?
Cell division is the process by which a cell divides into two new daughter cells. A cell replicates all of its DNA before division and each daughter cells receives its own genetic "library". In order to grow and divide, cells go through the cell cycle. A cell grows and divides to form two daughter cells which then start the cycle again. The cell cycle consists of four phases:
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II. What is mitosis?
Mitosis is divided into four phases: prophase, metaphase, anaphase, and telophase. This process allows the human body to grow and replace cells. The number of chromosomes are reduced by half through the separation of homologous chromosomes, producing two haploid "daughter" cells.
During the prophase, DNA molecules condense into chromosomes, the nuclear envelope breaks down and the spindle begins to form. The chromosomes line up in the center of the cell and each one is connected to a spindle fiber at its centromere in metaphase. During the anaphase, the spindle fibres shorten and sister chromatids separate into individual chromosomes. In the telophase, chromosomes gather at opposite sides and two nuclear envelopes form. |
III. What is meiosis?
Meiosis is the process of reproductive division in which the number of chromosomes per cell is cut in half through the separation of the homologuous chromosomes. The result is 4 haploid cells that are genetically different from the original cell.
In meiosis I, prophase I, the chromosome pairs form a tetrad with their corresponding homologous chromosome. Spindle fibers attach to the chromosomes during metaphase I. During anaphase I, chromosomes exchange portions of their chromatids in a process called crossing-over. The cells separate into two cells in telophase I. The first step of meisos II is prophase I, where the two daughter cells contain half the number of chromosomes as the original cell. During metaphase II, chromosomes line up in the center of each cell. The sister chromadits separate in anaphase II. The final result of meiosis II is four haploid daughter cells. |
IV. Mitosis v. Meiosis
A similarity between mitosis and meiosis is that the DNA is replicated in both phases in the beginning for the same reason. Cytokinesis occurs in telophase I and II in meiosis and it only occurs once in mitosis.The difference between are are that mitosis produces two daughter cells with identical sets of duplicate chromosomes and meiosis results in four haploid daughter cells with new combinations of alleles in the chromosomes. Mitosis allows the body to grow and replace cells, while meiosis is how sexually reproducing organisms produce gametes.
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