Short note on cell division.
Cell is the basic unit of life. When a cell reaches maturity, it divides to give rise to new cells of the same type. This process by which a cell divides to give rise to new cells is known as cell division.
Cell division can be described as the process of splitting up of the cell in to two daughter cells. They are two types of cell divisions:
1) Mitosis: Mitosis is the type of cell division where the daughter cells produced are exactly similar to the parent cell. They have the same chromosomal number as the parent cell. Mitosis occurs in all the somatic cells of the body. The phases of mitosis are:
a. Prophase: During this phase the nuclear membrane disappears and chromosomes appear. Centrioles move to the opposite corners and spindle fibre formation starts.
b. Metaphase: In this phase the chromosomes line up in the centre of the cell forming the equatorial plate. Spindle fibres attached to the centromere of the chromosomes.
c. Anaphase: In this phase spindle fibres are pulled back and sister chromatids of chromosomes are separated and move to the opposite ends of the cell.
d, Telophase: Nuclear membrane reappears around the chromosomes at both the ends, so two nucleuses are there by the end of this phase.
e. Cytokinesis: The cell divides forming two daughter cells containing one nucleus in each.
2) Meiosis: Meiosis is the type of cell division where the daughter cells produced are not similar to the parent cell. It is also known as reductional division where the chromosomal number of daughter cell is half the chromosome number of the parent cell. It occurs only in the reproductive cells of the body at the time of gamete formation. Meiosis occurs in two parts Meiosis I and Meiosis II.
Phases of Meiosis I:
a. Prophase I: During this phase the nuclear membrane disappears and chromosomes appear. Homologous chromosomes pair up and crossing over takes place.
b. Metaphase I: In this phase the chromosome pairs line up in the centre of the cell. Spindle fibres attached to the centromere of the chromosomes.
c. Anaphase I: In this phase spindle fibres are pulled back and homologous chromosomes are separated and move to the opposite ends of the cell.
d. Telophase I: Nuclear membrane reappears around the chromosomes at both the ends, so two nucleuses are there by the end of this phase.
e. Cytokinesis: The cell divides forming two daughter cells containing one nucleus in each.
Phases of Meiosis II occurs in each of the two daughter cells formed by meiosis I. It is similar to mitosis. The end result of meiosis is four haploid daughter cells.
a. Prophase II: During this phase the nuclear membrane disappears and chromosomes appear. Centrioles move to the opposite corners and spindle fibre formation starts.
b. Metaphase II: In this phase the chromosomes line up in the centre of the cell forming the equatorial plate. Spindle fibres attached to the centromere of the chromosomes.
c. Anaphase II: In this phase spindle fibres are pulled back and sister chromatids of chromosomes are separated and move to the opposite ends of the cell.
d. Telophase II: Nuclear membrane reappears around the chromosomes at both the ends, so two nucleuses are there by the end of this phase.
e. Cytokinesis: Each cell divides forming two daughter cells containing one nucleus in each. So, a total of four cells are formed.
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