Principles of Cell Division
Cell division is needed for growth and reproduction of all living organisms. New cells are produced from existing cells and it is helpful for various body parts to grow and replace damaged cells. Cells divide in reproduction to form gametes (sex cells). These female and male sex cells fuse to form the zygote, which develops into a new individual.
Human body cells have 46 chromosomes. They exist as 23 pairs of chromosomes. Similar chromosomes are paired and are known as homologous pairs. There are two copies of each chromosome. Homologous pairs carry the same features with same sequences. The body cells that contain homologous chromosome pairs are known as diploid cells (2n). Diploid cells are required growth and replacement of damaged cells. In the reproduction, gametes are produced. These gametes contain half a number of chromosomes as a normal body cell (also known as a somatic cell). The sex cells have 23 chromosomes which are not paired. Therefore, there is only one copy of a chromosome in a cell and those cells are known as haploid cells (n).
There are two types of cell division:
In mitosis, two identical nuclei are produced followed by immediate cell division. The daughter cells are similar in the type and number of chromosomes to each other and to the original (parent) cell. Mitosis occurs in unicellular organisms to increase their population. Also, all the cells in our body are produced by mitosis except sex cells. In meiosis, four cells are produced and they have half the number of chromosomes as the original cell. Only sex cells are produced by meiosis. Two diploid cells are produced from a diploid parent cell in mitosis. Four haploid cells are produced from a diploid parent cell in meiosis.