Meiosis is the reductional divisions that occur in the sex cells for gamete formation in higher organisms and in the zygote or sporophyte for spore formation in lower plants. Significances of meiosis are:
(1) Maintenance of chromosome number:
Haplosis (meiosis and syngamy fertilization) are two cardinal points in the life cycle of diploid organisms. Haploid gametes fuse to form diploid zygotes, which develop into diploid organism. These organisms again produce haploid gametes by reduction division. Failure of meiosis would result in doubling of chromosome number.
(2) Maintainance of DNA amount:
The DNA amount in an organism is represented in C value. Amount of DNA in the cells of diploids is 2C, which increases to 4C during S-phase of cell cycle by DNA replication. During meiosis, this value reduces to 2C after meiosis I and to C in gametes after meiosis II.
1. It occurs in meristemic cells.
2. Cell divides only once and produces two daughter cells having same chromosome number as in parent cell.
3. It helps in growth, development and replacement of damage tissues.
4. Prophase is of short duration and is not divided into sub-stages.
5. No genetic exchange occurs during prophase.
1. It occurs in reproductive cells.
2. Cell divides twice and produces four daughter cells, each containing half of the chromosomes of the parent cell.
3. It helps in sexual reproduction and multiplication of organisms.
4. Prophase-I is of long duration and is further divided into sub-stages.
5. Genetic exchange occurs between homologous chromosomes in prophase-I by crossing over.