The process of cell division for the production of gametes is called meiosis. In human beings and animals meiosis takes place in the testes and the ovaries. In plants meiosis take place in the anthers and ovaries.
Meiosis results in gametes which have half the number of chromosomes present in the parent cell. This is necessary so that when two gametes fuse in fertilization , the original number of chromosomes in the parent cell is obtained.
The original number of chromosomes in a parent cell before meiosis is known as the diploid number ( 2n chromosomes). The number of chromosomes in a gamete at the end of meiosis is called the haploid number ( ( n chromosomes ).
Each parent cell in meiosis produces four gametes with different combinations of chromosomes because the chromosomes are reshuffled during meiosis.
Importance of Meiosis
1. Production of gametes .
Meiosis enable the production of gametes, fertilization cannot take place without the presence of male and female gametes and new organisms cannot be produced.
2. Reduction in chromosome number.
Each gamete has only half of the number of chromosomes of the parent cell. This is necessary because fertilized ovum contains chromosomes from both the male and female gamete.
3. Maintainence of chromosome number in somatic cells.
Meiosis enable us to maintain the number of chromosomes in our somatic cells at 46 chromosomes.
4. Production of variation.
Meiosis causes genetic variation in the descendants. New individuals do not resemble their parents closely.
This is brought about in two ways:
(a) Different combinations of chromosomes due to reshufflement of parental choromosomes during meiosis process.
(b) Crossing over which took place when chromosomes are arranged along the equatorial plane. In the process the chromatids exchange genes and so increase genetic variation. Genetic variation in a species enables the species to survive.