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| Summary |
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 According to the modified cell principle, new cells arise only from pre-existing cells. |
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 Cells transfer their genetic information only by way of cell division. |
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 The mode of cell division is largely the same in all living organisms indicating the unity of life. |
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 Cell division becomes necessary for reproduction, growth, repair and regeneration. |
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 Cell division in eukaryotes is mainly of two types - mitosis, meiosis. |
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 Some primitive animals exhibit another kind of cell division called amitosis in which nucleus simply elongates and splits into two. |
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 Every cell capable of dividing, has a cell cycle. Consisting of three main stages namely interphase, karyokinesis and cytokinesis. |
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 Length of the cell cycle depends on nature of the cell, food, oxygen and other nutrients. |
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 Mitosis is the most common type of cell division. It is important in growth, reproduction, regeneration and repair. |
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 Mitosis occurs in all the living cells of the body of an organism. Hence it is called somatic cell division. |
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 Mitosis is described as equational division since the chromosome number of daughter cells will be same as that of the parent cell. |
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 Mitosis has an interphase, karyokinesis and cytokinesis. |
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 In the interphase, there is synthesis of reserve food and replication of DNA. |
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 Karyokinesis involves a series of changes leading to splitting and separation of chromosomes. It has four stages: prophase, metaphase anaphase and telophase. |
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 Cytokinesis involves division of the cytoplasm leading to separation of the daughter cells. |
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 Meiosis is a type of cell division, which occurs only in the reproductive cells, only during sexual reproduction. Hence, it is also called as germ cell division. |
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 Meiosis is described as reductional division since the chromosome number of the daughter cells is reduced to half (haploid) that of the parent cell (diploid). |
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 Meiosis has two successive nuclear divisions; hence it is divided into two stages: Meiosis-I and Meiosis-II |
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 Meiosis-I results in the formation of two haploid cells with half the number of chromosomes, but there is no reduction in the amount of DNA. It has a karyokinesis-I and a cytokinesis-I. |
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 Karyokinesis-I of first meiotic division can be distinguished into prophase-I, metaphase-I, anaphase-I and telophase-I. |
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 Prophase-I shows significant changes in the behaviour of chromosomes. On this basis it can be divided into five-sub stages leptotene, zygotene, pachytene, diplotene and diakinesis. |
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 During prophase-I there is pairing of homologous chromosomes, followed by crossing over and separation leading to genetic recombinations. |
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 Meiosis-II is almost a repetition of mitosis, except that there is no replication of DNA prior to prophase-II. |
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 At the end of meiosis, four daughter cells, each with haploid number of chromosomes and half the amount of DNA, are formed. |
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 Meiosis is necessary for the formation of spores and gametes. It is significant in contributing to the maintenance of a species-specific chromosome number. |
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