Mitosis and meiosis are processes that results in new cells that arise from one original cell. The purpose of mitosis is to increase cell number and this occurs by DNA replication by the original diploid (2 sets of chromosomes=2n) cell, which is then split into two cells. Each cell has equal amount of DNA and cellular organelles. Mitosis is necessary for multiple reasons in multi-cellular organisms. One example is that mitosis is essential for maintaining tissues, as cells naturally die or can be damaged and must be replaced. Another example is during development, when a fetus must continually grow into its adult form. The purpose of meiosis is to divide a diploid cell into a haploid cell (one set of chromosomes=1n) in order for sexual reproduction. Meiosis has similar steps as mitosis, as the original cell must first replicate its DNA and then divide into two cells with equal amounts of DNA and organelles. However, instead of stopping there, the two cells then divide without replicating DNA, resulting in 4 cells that are haploid. During sexual reproduction, two haploid cells, one from each parent organism, must join together during fertilization. When fertilzation occurs, the DNA from each haploid cell joins to form a diploid cell. Mitosis then causes the cell to divide and increase in cell number as the fetus grows. Without meiosis, sexual reproduction would rarely occur as it is the main tool that plants and animals use in order to produce offspring and to introduce genetic variability to the offrsping. Asexual reproduction does occur and does result in offsrping, but the offsrping are exact copies of the parent and there is no genetic variability, which can be detrimental in the long-run.
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