Cell division is a necessary step for the continuation of life. It is beneficial not only for the generation of new cells but also for the growth and development of existing cells. Mitosis and Meiosis are the two main forms of cell division that can take place. Several traits, as well as the fundamental definitions and the distinction between mitosis and meiosis, will be discussed in this section. Cell reproduction is the process of producing new species from a single-parent cell that has undergone asexual reproduction. Unicellular creatures and multicellular organisms, on the other hand, go through a distinct procedure. Cell division or reproduction is carried out by unicellular organisms in order to produce daughter cells. Cell division is carried out by multicellular organisms in order to promote growth and replace worn-out cells in the body. To put it another way, mitosis is the process of creating new body cells, whereas meiosis is the process of producing sperm and egg cells.
Mitosis
A complete copy of the genetic material is passed down to each daughter cell during mitosis, which is accomplished through the division of DNA into chromosomes (or genome). Organisms that reproduce sexually have two copies of each chromosome, one from their father and one from their mother, and they have two copies of each chromosome from their father.
Stages of Mitosis
The cell spends the majority of its time in the interphase, which occurs just before prophase and during which preparations are made for the onset of mitosis (the DNA is copied). Prophase, on the other hand, is technically the first stage of this process because the actual process involves the splitting of the nucleus.
The following are the several stages of mitosis that take place during cell division:
Interphase
A cell’s growth is halted during the interphase phase, which occurs just before it enters mitosis. When it is in interphase, it goes through the following phases:
- G1 Phase: This is the period of time preceding the production of DNA in the cell.
- S Phase: This is the phase of the cell cycle during which DNA synthesis occurs.
- G2 Phase: This is the stage of the cell cycle that occurs between the completion of DNA synthesis and the onset of prophase.
Prophase
Following the S and G2 phases of the cell cycle, prophase is characterised by the condensing of genetic material to create compact mitotic chromosomes, which are made of two chromatids connected at the centromere of each chromosome.
After prophase has been completed, the mitotic spindle, microtubules, and proteinaceous components of the cytoplasm that aid in the process are assembled, and the cell is ready to enter metaphase.
The nuclear envelope begins to disintegrate as a result of this.
Prometaphase
The nuclear envelope disintegrates during the prometaphase of the cell cycle. From the centromere to the chromosome, microtubules are now free to expand their reach further. The microtubules are attached to the kinetochores, which allow the cell to move the chromosome around in the cell space.
Metaphase
This is the stage at which the microtubules begin to tug the chromosomes with equal force, and the chromosome eventually ends up in the middle of the cell. The metaphase plate is the name given to this period of the cell cycle. As a result, each cell receives a fully functional genome.
Anaphase
Anaphase begins with the division of the sister chromatids, which signals the beginning of the cell cycle. In each daughter nucleus, these sister chromatids join together to form the chromosome. Chromosomes are then dragged towards the pole by fibres that are connected to the kinetochores of each chromosome, which is the most extreme position. The centromere of each chromosome is near the border of the chromosome, while the arms are trailing behind.
Telophase
As the nuclear membrane begins to form around the nucleus, the chromosomes that are clustered at the two poles begin to coalesce into a single undifferentiated mass. The nucleolus, Golgi bodies, and endoplasmic reticulum complex, which had vanished during prophase, have begun to resurface. Telophase is followed by cytokinesis, which is the splitting of the cytoplasm into two daughter cells, which occurs after the telophase. As a result, it signifies the completion of cell division.
Meiosis
It is necessary to use a certain type of cell division to make sex cells, such as sperm and eggs, which contain just one copy of each chromosome. The fusion of the sex cells results in the formation of a new individual that has two copies of each chromosome.
Many single-celled creatures reproduce through cell division and have only one copy of each chromosome, which is common in the animal kingdom.
Meiosis I: Reductional Cell Division is the first stage of the cell division process.
When it comes to cell division, mitosis is an equational process, whereas meiosis is a reduction process. The following are the distinguishing characteristics of meiotic division that distinguish it from mitosis:-
Meiosis I and Meiosis II are the two stages of nuclear and cellular division that occur throughout the process of cell division. DNA replication, on the other hand, occurs only once.
It is characterised by the pairing of homologous chromosomes and the occurrence of recombination between them.
At the end of the process, four haploid daughter cells are created, as opposed to two diploid daughter cells in mitosis.
Meiosis 1 is characterised by the separation of a pair of homologous chromosomes and the reduction of a diploid cell to a haploid. A woman’s menstrual cycle is divided into various stages, the most notable of which are the prophase, metaphase, and anaphase.
Phases of Meiosis 1
Meiosis 1 Prophase 1
Prophase I is longer than the mitotic prophase and is further subdivided into 5 substages,
- leptotene
- zygotene
- pachytene
- diplotene
- diakinesis
- It is during the period of leptotene that the chromosomes begin to condense and form a compact shape.
- Chromosomal synapsis is a process that occurs in zygotene that is marked by the pairing of homologous chromosomes, which is followed by the creation of a complex structure known as the synaptonemal complex. A bivalent or tetrad complex is formed when a pair of synapsed homologous chromosomes join together.
- Crossing over of non-sister chromatids of homologous chromosomes occurs at the recombination nodules during the pachytene stage of development. The chromosomes remain linked at the points where they crossed over to the other side.
- Diplotene is a chemical that indicates the dissolution of the synaptonemal complex and the separation of the homologous chromosomes of the bivalents, with the exception of the sites of cross-over between the bivalents. Chiasmata are X-shaped formations that emerge as a result of the separation of two atoms.
- Diakinesis is characterised by the closure of chiasmata and the formation of the meiotic spindle, which is responsible for separating homologous chromosomes. The nucleolus is no longer present, and the nuclear envelope is no longer whole.
Meiosis 1 Metaphase 1
After aligning at the equatorial plate, microtubules from the opposing poles attach themselves to the pairs of homologous chromosomes that have aligned with them.
Meiosis 1 Anaphase 1
Each bivalent’s two chromosomes separate and migrate to the opposing ends of the cell, creating a bivalent. The sister chromatids are physically connected to one another.
Meiosis 1 Telophase 1
The nuclear membrane returns, and cytokinesis occurs as a result of this. This results in the formation of a pair of cells.
Conclusion
To summarise, Mitosis and Meiosis are cell division processes that are beneficial to our everyday lives. It is impossible for cells to reproduce unless they go through the processes of meiosis and mitosis. In addition, genetic variety and cell development would be impossible to achieve. During mitosis, the goal is to form daughter cells that are genetically identical to their mothers, differing only in the presence or absence of one chromosome. When it comes to the human body, meiosis serves a single purpose: it is responsible for the formation of gametes, which are sexual cells such as sperm and eggs.