Why is Meiosis important to Living Things?
Meiosis is one type of cell division that occurs in diploid organisms at the time of sexual reproduction. Mitosis is the type of cell division which occurs when the body cells divide for growth purpose or when any injured tissue has to recover from damage. Meiosis division takes place in two major steps called as meiosis I and meiosis II. Meiosis I constitute prophase I, metaphase I, anaphase I and telophase I. Meiosis II constitutes prophase II, metaphase II, anaphase II and telophase II. Meiosis I occurs with reduction in the number of chromosomes which were united when the two gametes from the parent cells were fertilized. The reduction division will be followed by the normal mitotic division or meiosis II. Meiosis II is similar to mitosis and it results in 4 offspring cells each of which have haploid nucleus.
After fertilization, each of the haploid gametes containing 23 chromosomes each united to form the zygote that consists of 46 chromosomes. Each of the 46 chromosomes pairs with their corresponding homologous chromosomes. In each pair of homologous chromosome, the chromosome splits into two chromatids. Each of the pairs will have four chromatids. Crossing over occurs in between the genetic segments of chromatid of one chromosome and the chromatid of another chromosome. Exchange of genetic segments will lead to the evolution of specific visual changes in the species. The exchange occurs in prophase I. The tetrads are arranged in the center of the cell in metaphase I. In anaphase I, 23 chromosomes will be dragged to one pole of the cell while 23 chromosomes to the other pole. As the chromosome number is reduced from 46 to 23, this type of division is called the reduction division. The telophase I forms two cells with 23 chromosomes and 46 chromatids in each cell. Meiosis II divides the 46 chromatid cell into two cells having 23 chromatids. Since there are two cells available after meiosis I, altogether four cells having 23 chromatids or chromosomes are formed. Hence, they are called as haploid cells.
If reduction division does not occur, the organisms in each generation will increase the chromosome number exponentially and the offsprings will become polyploids. Moreover, meiosis has to occur to introduce variations in the species, within the genus, families and so on. Acclimatization and adaptability of organisms to the environment happen by genetic variations too. So, meiosis is important for living organisms.