Introduction
Cell division is an important process in all living forms. In biological studies, two types of cell division have been identified namely mitosis and meiosis. In this paper, the discussions shall focus on the differences between these two types of cell division plus the various steps involved in each of these cell division processes.
Stages of Cell Division in Mitosis and Meiosis
Mitosis
Mitosis is both a nuclear and a cytokinesis cell division process that produces two daughter cells that are genetically similar. It has five phases namely, prophase, prometaphase, metaphase, anaphase, and telophase (Imoto et al, 2011). Interphase is also included as the first stage of cell division since it shows the period in which the cell undergoes growth in preparation for the division.
Delegate your assignment to our experts and they will do the rest.
Interphase : Apparently, interphase is often included in mitosis discussions but it is not part of the mitosis process. However, it is included in the discussions since it encompasses three stages which are integral in the cell cycle. These are G1, S, and G2 phases. G1 is the period before the synthesis of DNA. The G1 means the first gap phase. Under this phase, the cell mass increases in readiness for cell division. The S phase is the DNA synthesis phase (Imoto et al, 2011). The s stands for synthesis. G2 refers to the period after DNA has been synthesized but before the commencement of the prophase. During this time, the cell continues to synthesize proteins hence its size keeps on increasing. Notably, G2 phase stands for the second gap phase. At interphase, the nucleolus of the cell is still present and the nucleus appears to be enclosed in a nuclear membrane. The chromosomes, on the other hand, have duplicated but appeared like chromatin. In animals, centrioles will form after the replication and will be found on the nucleus periphery.
Prophase: During this phase, the nucleus condenses and the chromosomes become visible under a light microscope. The nucleolus of the cell disappears and the centrioles move to different poles of the cell. Spindle fibers will be attaching the chromosomes at the centromere while other fibers will be crossing the cell forming the mitotic spindle fibers.
Prometaphase: In this stage, the nuclear membrane disappears. Apparently, this marks the onset of the prometaphase. Proteins will be attached to the centromere to form kinetochores (Imoto et al, 2011). Afterward, microtubules become attached at the kinetochores. The final change is noted with chromosomes beginning to move towards the center of the cell.
Metaphase: At this phase, the spindle fibers become fully formed. With the spindle fibers attached at the centromere, the chromosomes become arranged at the equator of the nucleus of the cell forming a line known as the metaphase plate. This organization ensures that when the chromosomes become separated in the next phase, each nucleus formed receives a copy of each of the chromosomes in the cell.
Anaphase: In this phase, the paired chromosomes begin to separate at the kinetochore and move in opposite poles of the cell. The combination of the kinetochore movement along the spindle fibers and the interactions of the polar microtubules results to the motion noted on the chromosomes. The spindle fibers that are not connected to the chromatids are responsible for lengthening and elongating the cell. The end of the anaphase phase a complete compilation of the chromosomes will be contained at each pole. Notably, the process of cytokinesis begins at this phase and proceeds in the telophase. Cytokinesis is the division of the cytoplasm of the cell.
Telophase: This phase is marked by the chromatids arriving at the opposite ends of the cell pole. A new cell will be formed around each of the daughter cell nuclei. In addition, the chromosomes disperse as a result they cannot be seen under a light microscope. Just like the chromosomes, the spindle fibers also disperse. Cytokinesis which is denoted by partitioning of the cell becomes apparent during this phase (Imoto et al, 2011). At the end of this process, the mitotic process is almost complete since the genetic material of one cell would have been equally divided into two.
Cytokinesis : As aforementioned, cytokinesis refers to the process in which the cell cytoplasm divides. It often commences before the end of the mitosis process in anaphase. It then proceeds to telophase phase where it is completed. At the end of this process, two daughter cells with the identical genetic material are produced. In cells of animals, cytokinesis begins when actin contracts to cause the cell to form two daughter cells with each cell containing one nucleus. Notably, actin is a fiber protein that forms around the cells center. In cells of plants, a cell plate is first formed between the two daughter cells. This is because plant cells have a cellular cell wall and animal cells lack the cellular cell wall.
Diagrammatic illustration of Mitosis
Meiosis
Meiosis, as mentioned earlier, is a type of cell division that takes place during the process of gamete formation. Normally, the process halves the number of chromosomes and yield four gametes at the end. This process has been integral in the production of eggs and sperm cells during sexual reproduction. Essentially, the number of chromosomes is restored to 46 once the sperm and the egg fuse to form a single cell. The process of meiosis usually begins with a diploid parent cell. This implies that the parental cell contains the two chromosomal copies (Miko, 2008). During meiosis, the parent cell undergoes a one round replication of the genetic material. Nuclear division will then follow this process. The division will take place in two distinct cycles. The end result of this process is four haploid daughter cells. This implies that the number of chromosomes in the daughter cells will be half the number of parent cell.
Meiosis and mitosis processes have some common features and differences. For instance, mitotic division produces diploid daughter cells while meiosis produces diploid daughter cells. The process of meiosis has been divided into two stages namely meiosis I and Meiosis II. Each of these stages has a number of phases. Meiosis I refer to division of the cell which is particular for germ cells while the activities in meiosis II correspond to those of mitosis.
Notably, Meiosis I is referred to as the first meiotic division. It commences with Prophase I. In this phase, the DNA and chromatin condense to form a threadlike structure called the chromosomes. Replicated pairs of chromosomes are normally referred to as chromatids. Chromatids are joined together at a particular point called the centromere (Miko, 2008). In addition, a structure called mitotic spindle is formed from microtubules and they are found on the opposite poles of the cell. Apparently, pairs of chromosomes form tetrads between Prophase I and metaphase I. within each tetrad, any pair of the chromatid arms can overlap and fuse.
This process is what scientists refer to it as recombination or crossing-over. Basically, recombination refers to a process in which a section of the DNA breaks, recombines and rejoins to produce new genetic combinations.
Metaphase I is characterized by homologous chromosomes aligning on opposite sides of the equatorial plate. The events proceed to anaphase I where the spindle fibers contracts and pull the homologous pairs in two opposite directions. The homologous chromosomes will move away from one another towards the opposite poles of the cells with each having chromatids. In the telophase I phase, the chromosomes become enveloped in nuclei. The cell finally undergoes cytokinesis where the parental cell cytoplasm divides to produce two daughter cells. in this case, the produced daughter cells are haploid in nature. This implies that the number of chromosomes they contain is half that of the parental cell.
The phases in Mitotic II resemble those of mitosis. The difference is that meiosis II proceeds with haploid cells that were produced in the first meiotic stage. In prophase II, the chromosomes condense and become visible. Spindle fibers develop and the chromatids start moving towards the cell’s equator. In metaphase II, the chromatids (paired) will have their centromeres aligned at the equatorial plates in each of the daughter cells (Miko, 2008). The next phase is the anaphase II which is characterized by chromosomes separating at the centromeres. The spindle fibers condense and pull the chromosomes towards the opposite ends of the cell. At telophase II, the chromosomes reach the cellular pole and are enveloped in nuclear membranes. Finally, cytokinesis follows which leads to division of the cytoplasm of the two cells. At the end of this process, four daughter cells will be produced which are haploid in nature. The daughter cells will develop into either form sperm or egg cells.
Diagrammatic illustration of the meiotic process
In conclusion, mitosis is a type of cell division that leads to the formation of new body cells. It is an important process since it helps in the repair process in living organisms such as healing of wounds. Mitosis is a crucial process in life. It ensures that the cell contents are duplicated. Notably, the chromosomes split or rather divide to produce two identical daughter cells. Due to the importance of this process, a particular number of genes regulate the various steps involved. Failure to control this process correctly leads to the development of health complications such as cancer. On the other hand, meiosis refers to a type of cell division that takes place during the formation of egg cells, sperm cells, and spores. Meiosis serves to ensure that the number of chromosomes is maintained in each generation. Basically, meiosis takes place in two processes. In the first process, the number of chromosomes is halved to form gametes. When the gametes fuse at conception, each of them contributes 23 chromosomes so that the resulting embryo contains the usual number (46) of chromosomes. Besides, meiosis allows species to exhibit variation due to the process called DNA recombination or rather crossing over during the cell division process.
References
Imoto, Y., Yoshida, Y., Yagisawa, F., Kuroiwa, H., & Kuroiwa, T. (2011). The cell cycle, including the mitotic cycle and organelle division cycles, as revealed by cytological observations. Journal of electron microscopy , 60 (Suppl 1), S117-S136.
Miko, I. (2008). Mitosis, meiosis, and inheritance. Nature Education , 1 (1), 206.
