MITOSIS (M PHASE)
$\displaystyle \small \bullet$ Mitosis cell division is also known as equational division because the numbers of chromosome remain same in parental and progeny cells.
$\displaystyle \small \bullet$ M phase is divided into four phases - Prophase, Metaphase, Anaphase, Telophase
Prophase
1. It is the first stage of cell division and the longest phase
2. In this stage the condensation of chromatin or DNA occurs
3. Chromosomes appear as pairs of chromatids joined by centromere
4. Nuclear membrane begins to disintegrate
5. Nucleolus start disappearing
6. Centrioles move to opposite poles
7. Formation of spindle fibres, radiating from centrioles
1. Complete disintegration of nuclear membrane and chromosomes are spread in the cytoplasm
2. Condensation of chromosome completes and they are clearly observed under microscope
3. All chromosomes arranged at the equator forming equatorial or metaphase plate
4. Centriole(asters) are at the opposite pole.
5. Each chromosome consist two sister chromatids
1. Chromatids are separated by splitting of centromere
2. Daughter chromatids move towards opposite pole by shortening of spindles
3. Separation of chromatids form the chromosomes
4. Chromosomes move away from equatorial plate
1. Chromosomes reach the opposite pole of the cell
2. Chromosome uncoil and form chromatin network
3. Spindle fibres disintegrate
4. Centrioles replicate in animal cell
5. Nucleolus reappears, cell organelles reformed
6. Completion of nuclear division.
7. Telophase leads to cytokinesis
$\displaystyle \small \bullet$ Cells divide itself into two daughter cells.
$\displaystyle \small \bullet$ In animal cells, the cell membrane begins to constrict and a furrow is formed at the middle of cell in the telophase. The furrow deepens and the cell membrane of opposite side joins in the centre. It forms two daughter cells.
$\displaystyle \small \bullet$ In plant cells, cytokinesis begins by the formation of cell plate. The protein fragmoplast secretes and deposited in the equatorial plane form a cell plate. The cell plate represents the middle lamella between the walls of adjacent cells.
$\displaystyle \small \bullet$ In some organisms, karyokinesis is not followed by cytokinesis as a result of which multinucleate condition arises leading to the formation of syncytium. Example: liquid endosperm in coconut.
$\displaystyle \small \bullet$ Mitosis results in the production of diploid daughter cells with identical genetic complement.
$\displaystyle \small \bullet$ The growth of multicellular organisms is by the mitosis.
$\displaystyle \small \bullet$ It is essential for the cell repair. The cells of the upper layer of the epidermis, cells of the lining of the gut, and blood cells are being constantly replaced.
$\displaystyle \small \bullet$ Mitotic divisions in the meristematic tissues (the apical and the lateral cambium), result in a continuous growth of plants throughout their life.
$\displaystyle \small \bullet$ Since mitosis does not cause any genetic variation, it maintains the originality of the organism type from generation to generation.
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