The title “We are never ever, ever getting back together- cell division” means that the two daughter cells formed as a result of Mitosis never going to return to become parent cells again. This article focuses on mitotic cell division.
To read the introductory part of cell division, go through the link –https://www.anthromania.com/2021/06/16/how-cells-in-our-body-divide/
Mitos means thread or fibril. Mitosis term is given by Flemming (1882).
Mitosis, also known as Equational Division or Somatic cell division refers that chromosomes equally distributed both quantitatively and qualitatively from parent cells to two daughter nuclei. This division maintains the chromosome number for generations.
Mitosis involves the division of the nucleus which is followed by the division of the cytoplasm. When the cell is not ready to divide then it is known as the Interphase stage. During this phase, chromosomes are not clearly visible.
An elaborate process is necessary for forming two daughter cells out of the parent cell. The whole process is studied under 4 stages–
Chromosomes are visible as long, slender and coiled threads. They get shortened and thicken.
Each chromosome is seen to be made of two identical strands known as Chromatids lined against each other throughout the length. A chromosome bears a constriction, a region of attachment of two chromatids at a single point known as centromere or kinetochore.
During this stage, the nucleus and nuclear membrane disappear and a spindle shape body known as a nuclear spindle or mitotic spindle is formed.
As prophase advances, the chromatids become closely coiled and the double nature of chromosomes disappears.
During this phase, the chromosomes are radially oriented in the equatorial plane. The two chromatids lie parallel to each other. The spindle extends into the nuclear area and occupies the centre of the cell. The spindle gets attached to the centromere. Fibres of the spindle that are attached to chromosomes are called chromosomal fibres (discontinuous fibres or tactile fibres) while others are known as continuous fibres.
In this stage, the chromosomes begin to disappear. Each centromere divides equally. First, the two centromeres and later on the chromatids are pulled apart. The two halves or identical sets of chromatids move to the opposite poles of the spindle. Thus the two chromatids become separated from each other. Each group contains the same no. of chromosomes.
It is the reverse of prophase. During this phase, a nuclear envelope forms around each group at the opposite poles. The spindles disappear. Now the cell membrane gets constricted in between which results in the formation of two daughter cells. Each daughter cell has the same amount of cytoplasm and nucleus.
Significance of mitosis
- Equal distribution of chromosomes in the daughter cells in terms of quality and quantity.
- Maintains a constant no. of chromosomes from generation to generation in all body cells of an organism.
- Maintains purity of gametes.
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