Meiosis Cell Division

The process by which a cell divides into two daughter cells is known as the cell cycle. In this process, the genome is duplicated, and other constituents of the cell are synthesized. Cell growth is a continuous process, but the synthesis of DNA synthesis takes place only at a specific phase in the cycle. Then, the duplicated chromosomes are distributed to the daughter cells by a sequence of events during cell division. These events take place under the control of genetics. Cell division can occur in two ways: Mitosis and Meiosis. What is meiosis, and what are the stages of meiosis are explained below.

What is Meiosis

Meiosis is a type of cell division in which a single cell divides twice to produce four cells. The cells contain half of the initial amount of genetic information. These cells are reproductive cells, i.e. sperms in males and eggs in females. The formation of the haploid phase in organisms demonstrating sexual reproduction occurs through meiosis, while the diploid phase gets restored by fertilisation. We come across meiosis during gametogenesis in plants and animals. This leads to the formation of haploid gametes. There are two stages of meiosis. These are two cycles of cell division that occur in a sequence. These stages are called meiosis I and meiosis II. However, DNA replication takes place in a single cycle. 

Meiosis I

Meiosis I happens in four phases:

• Prophase I: In this phase, the duplicated chromosomes turn into X-shaped formations. Each chromosome is made up of two chromatids having similar genetic information. The pairing up of chromosomes takes place. By the end of this phase, the meiotic spindle gets assembled to form separate chromosomes. When the prophase I phase finishes, the membrane around the nucleus dissolves and the chromosomes are released.

• Metaphase I: In this phase, the chromosomes get aligned around the centre of the cell, called the equatorial plate. The meiotic spindles extend from the centrioles, which are now placed opposite to each other at the poles of the cells. The fibres of meiotic spindles get attached to one chromosome in each pair.

• Anaphase I: In this phase, the pair of chromosomes are separated by the meiotic spindle. The meiotic spindle draws one of the chromosomes to one pole and the other one to the opposite pole of the cell. Unlike mitosis and meiosis II, the sister chromatids stay connected in anaphase I.

• Telophase I: In this phase, the chromosomes have their final movement towards the opposite cell poles. A complete set of chromosomes assemble at the cell poles. Two new nuclei are formed by the creation of a membrane around every set of chromosomes. The single cell is then divided from the middle and produces two different daughter cells. Each daughter cell contains a nucleus having a complete set of chromosomes. This is called cytokinesis.

Meiosis II

Meiosis II takes place in four phases:

• Prophase II: In this phase, there are two daughter cells with 23 chromosomes each. The chromosomes of both the cells turn into X shaped formations. The membrane around the nucleus dissolves, and the chromosomes get released. There is a creation of duplicate centrioles, and the meiotic spindle gets produced again.

• Metaphase II: In this phase, the chromosomes get aligned around the centre of the cell, called the equatorial plate in each daughter cell. The meiotic spindles are now placed opposite each other at the poles of the cells. The fibres of meiotic spindles get attached to each of the sister chromatids.

• Anaphase II: In this phase, the meiotic spindle acts and draws one of the sister chromatids to one pole and the other one to the opposite pole of the cell. The chromatids are dissociated and get formed into separate chromosomes.

• Telophase II: In this phase, the chromosomes have their final movement towards the opposite cell poles. A complete set of chromosomes assemble at the cell poles. Two new nuclei are formed by the creation of a membrane around every set of chromosomes. Then another cycle of cytokinesis occurs. Post that, four cells are produced, each containing one-half set of chromosomes. In males, these are the four sperm cells, while in females, one is an egg cell, and the other three are polar bodies, i.e. cells that do not get converted to eggs.

Conclusion

The process by which a cell divides into two daughter cells is known as the cell cycle. In this process, the genome is duplicated, and other constituents of the cell are synthesized. Cell division can occur in two ways: Mitosis and Meiosis. Meiosis is a type of cell division in which a single cell divides twice to produce four cells. The cells contain half of the initial amount of genetic information. These cells are reproductive cells, i.e. sperms in males and eggs in females. Meiosis takes place in the sequence of meiosis I and II. Meiosis I consists of Prophase I, Metaphase I, Anaphase I and Telophase I. Meiosis II consists of Prophase I, Metaphase I, Anaphase I and Telophase I.