Difference Between Mitosis and Meiosis

Comparing mitosis and meiosis side by side makes their very different biological roles clear. Structurally, plant and animal mitosis themselves already differ in some details: animal cells possess centrioles and form visible asters at the spindle poles, while plant cells lack centrioles and do not form asters; animal cells divide their cytoplasm by furrowing and cleavage using a contractile ring, while plant cells instead build a cell plate; and mitosis in plants occurs mainly at the meristem, whereas in animals it can occur in tissues throughout the body (Table 7.3). The deeper contrast, however, is between mitosis and meiosis as processes. Mitosis is a single division producing two daughter cells; meiosis comprises two successive divisions producing four. In mitosis the chromosome number stays the same in the daughter cells as in the parent; in meiosis it is halved. In mitosis, homologous chromosomes line up independently and separately on the metaphase plate, never pairing, so chiasmata never form and crossing over never occurs; in meiosis, homologous chromosomes actively pair up to form bivalents at metaphase I, chiasmata do form during prophase I, and crossing over occurs routinely. As a direct consequence, the daughter cells of mitosis are genetically identical to the parent cell and to one another, while the daughter cells of meiosis are genetically different both from the parent cell and fro …