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Mitosis is a type of cell division by which a eukaryotic cell divides into two by a special method. In this process, the nucleus and chromosome are divided once and the number, structure and properties of the chromosome in the newly formed cell remain just like the mother. cell. Mitosis is also termed as equational division. Normally this division occurs in the somatic cell. As a result of this division, the plant and animal increases in length and breadth. Mitosis occurs in all meristematic cells of plants.
The chromosomes are duplicated just before mitosis, so there are two identical (‘sister’) copies of each one. This gives a total of 2 x 46 chromosomes (92). They remain in their ‘unwound’ state and are therefore invisible.
The centrioles, a pair of cylindrical structures, are also duplicated. Each set of centrioles is surrounded by a tubule-making zone; the centrioles and the zone together make up a centrosome.
Stages of Mitosis :
Mitosis is a continuous process. The process is completed by a complex method. According to the sequence and stages, this continuous process is divided into four stages.
The stages are:
The chromosomes become visible. The two identical copies of each chromosome are called chromatids. Each chromatid pair is joined together, forming an ‘x-shaped’ structure called a metaphase chromosome.
The nuclear membrane, nucleolus, endoplasmic reticulum and Golgi complex break up.
The centrioles move to opposite ends of the cell, and spindle fibres begin to grow out from them.
The chromosomes are now in the middle of the cell. Spindle fibres attached to chromatids.
The two sister chromatids are separated and pulled to opposite ends of the cell. As a result, each of the daughter cells from mitosis ends up with one copy of every chromosome that was in the original cell. The cell begins to pinch inwards in the middle.
The two sister chromatids from each metaphase chromosome are now at opposite ends of the cell. At the site of the metaphase plate, the cytoplasm pinches inward.
The cell is divided into two cells and mitosis ends. In each new cell, the nuclear membrane and other organelles begin to re-assemble and the chromosomes are ‘unwound’.
The result of mitosis is two cells that are identical to each other and the original cell.