A crucial part of the growth of different organisms throughout their life involves cell division. As self-explanatory as the term ‘cell division’ may seem, it does not only refer to the creation of new cells; it is critical for growth and development, too. Cell division is performed with the aim of helping in reproductive growth by the creation of sex cells and, of that, to elevate growth and development.
Mitosis vs. Meiosis
Mitosis is a form of cell division that creates new body cells, often known as cell duplication; meiosis, on the other hand, generates sex cells (eggs and sperm). In unicellular organisms, cell division or cell reproduction paves the way for the next generation. In the case of multicellular organisms, cell division also occurs for growth and development, along with producing a new organism.
Difference Between Mitosis and Meiosis in Tabular Form
|Types of organisms||Occurs in all organisms, apart from viruses||Occurs only in plants, animals and fungi|
|Function/Type of cells created||Creates somatic cells (for growth and repair)||Creates sex/germ cells|
|Number of divisions||One cell division||Two cell divisions|
|Number of total stages||4||8|
|Number of cells created||Two daughter cells||Four daughter cells|
|Genetics||The daughter cells created are genetically identical||Daughter cells created are genetically distinct|
|Length of prophase||Shorter than meiosis||Longer than mitosis|
|Frequency of occurrence in the body||Frequently||Takes place during gamete formation|
|Recombination/crossover||Absent||Present during prophase 1|
What is Mitosis?
Mitosis is a part of cell division or cell reproduction wherein a cell replicates its chromosomes, which then separates them, resulting in the formation of two identical daughter cells with identical genomes. Cells with very few or too many chromosomes mostly don't function well; they hardly survive or may even cause cancer. Mitosis is a crucial process due to its functions of elevating growth and replacing worn-out cells. This process is a major requirement for vegetative propagation in plants, asexual reproduction, and repair of damaged tissues.
Mitosis is often referred to as equational cell division, contributing to the fact that the number of chromosomes in the parent and daughter cells remains the same. The process of Mitosis happens in multiple stages, mainly - interphase, prophase, prometaphase, metaphase, anaphase, and telophase.
Stages of Mitosis
- Interphase: There are three sub-phases in the interphase. The G1 Phase denotes the period before the amalgamation of DNA. This phase is followed by the S Phase, in which the synthesis of DNA takes place. Followed by this comes the G2 Phase, which marks the end of the S phase and the beginning of the Prophase.
- Prophase: In prophase, cells begin to break down a few structures and pave the way for others to build up. This further sets the stage for chromosomes to start condensing. The mitotic spindle (a structure made of strong fibers that are a part of the cell's skeleton) starts to form. The function of the mitotic spindle is to organize the chromosomes during Mitosis. This is also the stage during which the nucleus prepares to break down.
- Prometaphase: The mitotic spindle starts to organize the chromosomes and the nucleus; the nuclear envelope separates. The mitotic spindle also grows more, while microtubules begin to capture chromosomes and extend toward the edge of the cell, resulting in the formation of a structure called the aster.
- Metaphase: Microtubules during this phase begin to pull the chromosome. Due to this, they end up in the middle of the cell, and each cell gets an entire functioning genome.
- Anaphase: The sister chromatids during this phase separate from each other, where each of them now functions as their chromosome and is pulled to the opposite ends of the cell.
- Telophase: This phase is witnessed by the disappearance of the spindle and the reforming of the nuclear membrane. The cell division nearly finishes, and its normal structure as cytokinesis, which refers to the process of division of the cytoplasm to form new cells, begins to re-establish. This entire process ends shortly after the telophase, and we finally have two new cells with identical chromosomes.
What is Meiosis?
Unlike Mitosis, Meiosis only has one function in our bodies, i.e., to produce gametes - sperm and eggs (or sex cells). Meiosis is also called reduction division, interestingly arising from the fact that the division of a germ cell with two fissions of the nucleus gives rise to 4 sex cells where each has half the number of chromosomes of the parent or original cell. During Meiosis, cell division takes place two times. We can understand it better by considering the case of chromosomes in most human cells. Each cell in the human body has 46 chromosomes; 23 chromosomes come from each of our parents, which together form a new cell (embryo). In simple words, each sperm and each egg carries 23 chromosomes each; when an egg and a sperm join during fertilization, the two sets of chromosomes form a complete one, a new cell.
Stages of Meiosis
Since cell division occurs twice in Meiosis, each cycle of division goes through four stages - Prophase, Metaphase, Anaphase, and Telophase. Let us go through these phases in detail in each cell division that takes place.
- Prophase: A cell goes through interphase before entering Meiosis. During the interphase, the cell grows, copies all of its chromosomes, and prepares for division. Once the prophase begins, the nuclear envelope starts to come apart, the chromosomes start condensing, and the spindle fibers start to appear.
- Metaphase: The equator of the cell is where homologous chromosomes—paternal and maternal copies of the same chromosome—align. Maternal and paternal chromosomes line up and randomly position themselves on each side of the equator in a process known as independent assortment. This ultimately establishes the allocation of gamete chromosomes, resulting in genetic variation among progeny.
- Anaphase: Here, the spindle fibers retract, pulling every homologous chromosome in the opposite direction to the cell's pole. This results in an equal division of the DNA between the two newly generated cells.
- Telophase: At last, during telophase I, when the chromosomes reach the cell's poles in opposition to one another, the chromosomes decondensed, and the nuclear membrane reform in some organisms. while in others, this stage is omitted because the cells will shortly undergo Meiosis II. When cytokinesis takes place, a pair of haploid daughter cells are typically formed at precisely the same time as telophase I.
- Prophase II: Prophases I and II are quite similar. The centrioles develop, and the nuclear envelopes vanish. Centromeres link the kinetochores of individual chromatids, which are connected by microtubules that stretch throughout the cell. The chromosomes start to gravitate in the direction of the metaphase plate.
- Metaphase: In metaphase II, the chromosomes line up one by one along the metaphase plate.
- Anaphase: In anaphase II, sister chromatids are separated, followed by them being toward opposite poles of the cell.
- Telophase: Similar to telophase I, the cell has now been divided into two, and the chromosomes have reached the opposite ends of the cell. Once the Cytokinesis or plasma division is over, new nuclear envelopes are created around the chromosomes. By the end of Meiosis II, we have 4 haploid cells. These can be later developed into sperms or eggs in males and females, respectively.
Main Difference Between Mitosis and Meiosis in Points
- The number of Chromosomes of the daughter cells in Mitosis is the same as that of the parent cell. During Meiosis, on the other hand, the number of Chromosomes is half the number of chromosomes in the parent cell, which results in haploid cells.
- A key difference between Mitosis and Meiosis is the occurrence of synapsis and crossing over. Synopsis refers to the pairing of homologous Chromosomes, which happens during the Prophase I of Meiosis. Synapsis and crossing over are absent in Mitosis.
- During the prophase of Mitosis, the Chromosomes condense, and the formation of spindle fibers takes place, while during the Prophase of Meiosis, synapsis and crossing-over occur.
- While Mitosis occurs in all cells, Meiosis occurs in only reproductive cells for sexual reproduction.
- Diploid daughter cells are created in Mitosis, unlike in Meiosis, wherein haploid daughter cells are formed
- Mitosis results in the formation of two daughter cells, while four daughter cells are formed as a result of Meiosis.
- The daughter cells formed are genetically identical in Mitosis and genetically un-identical in Meiosis, respectively.
- Cell division happens only once in Mitosis, while the same happens twice in the case of Meiosis.
The two forms of cell division, Mitosis and Meiosis, no matter how divergent they might be, are of paramount importance in human development. While Meiosis fulfills its job of creating genetic variation and reproductive purposes, Mitosis aids us with growth and development and, quite often, repairs genetic defects.