The general consensus within the scientific community is that the two most important processes of known life on Earth are undoubtedly that of mitosis and meiosis. Mitosis and meiosis are key to both cellular reproduction and the continued existence of life on Earth. Cellular reproduction as a process is crucial to organismal growth, evolution, and viability, as it is the duplication and division of cells. As important as mitosis and meiosis are in contributing to cell division, they both execute these divisions in different ways. However, notable comparisons can be made between the steps of both mitosis and meiosis. Although both vastly important for life on Earth, mitosis and meiosis can be compared and contrasted on several key points: the “being” phases, the results of each process, and the purposes at the organismal level.
Mitosis involves a parent cell dividing into two identical daughter cells, each one of which shares the same components, function, and chromosomal number as the parent cell. Mitosis occurs constantly in almost every cell in sexually reproducing organisms, especially when there is a great need for growth and repair within the organism in question (Reese, 2015). Mitosis is completed via five main phases, being interphase, prophase, metaphase, anaphase, and telophase. The second process, meiosis, is the method by which cells produce gametes, which are genetically unique haploid cells. Gametes are crucial to sexual reproduction in that two of them unite in order to form a zygote, which will eventually develop into a fully grown organism. (Scoville, 2017) With each round of meiosis, four genetically unique, haploid daughter cells are produced that have half the number of chromosomes as the parent cell. Occurring in the reproductive organs of sexually reproducing organisms, meiosis takes place at specific times during an organism’s development. Meiosis consists of two main phases, meiosis I and meiosis II, as well as subphases within these two divisions (Diffen, 2012). When combined, these two cellular processes are the backbone of the continued development and reproduction of life on Earth.
The first means of contrasting mitosis and meiosis comes from the results of each process. At the end of mitosis, two diploid cells are produced that are identical to both each other as well as the parent cell. During the earlier phases of mitosis, the cell’s DNA and organelles are reproduced exactly, and chromosomes separate so that each daughter cell will have the same amount. On the other hand, meiosis produces four genetically unique, haploid gametes. These genetic variations that can be seen in gametes result from random fertilization, crossing over, and independent assortment during the events of meiosis I, meiosis II, and eventual fertilization (Reese, 2015). The beneficial effects of these genetic variations are stated by H. Scoville, claiming, “However, mistakes in meiosis and the random mixing up of genes and chromosomes throughout the process do contribute to genetic diversity and drive evolution.” (Scoville, 2017, pg. 1). Random fertilization means that any egg cell can be fertilized by any sperm cell, increasing the number of genetic combinations that can present themselves. Independent assortment has to do with the way that homologous pairs of chromosomes (one chromosome from each parent of the organism) are lined up in the middle of the cell during metaphase, and then with how they are distributed to each of the future gametes at the end of anaphase and meiosis I (Diffen, 2012). During crossing over, nonsister chromatids exchange corresponding sections of DNA with each other during one of the initial phases of both mitosis and meiosis, prophase (Scoville, 2017). All of this contributes to the unique allele and gene combinations within each gamete, and having genetically unique gametes promotes genetic variation and variety between organisms of the same species. Halving the chromosome number ensures that the base number of chromosomes in an organism will not double with each successive generation, keeping the organism genetically viable (Biology, Boundless, 2018).
Mitosis and meiosis, while differing in events that occur during each important phase, can still be compared by their steps in reaching the final result. Both consist of five core phases that have roughly the same basic function. First is interphase, which is the first step of mitosis and meiosis and serves the purpose of duplicating the cell’s DNA and organelles while increasing its size. During prophase, chromatin, the material that composes chromosomes, condenses in order to form chromosomes in both cellular mechanisms (Biology, Boundless, 2018). In both mitosis and meiosis, metaphase involves the alignment of chromosomes along the metaphase plate via the mitotic spindle, which is a network of fibers that attach to the sister chromatids of the chromosomes (Scoville, 2017). During anaphase, the mitotic spindle pulls the sister chromatids apart during mitosis and homologous pairs of chromosomes apart during meiosis I. At the end of mitosis and meiosis I, telophase and cytokinesis work together in order to divide the parent cell into two daughter cells. At this point, the processes begin to differ, as meiosis II begins at the point that mitosis would end. Throughout the steps of meiosis II, the centromeres holding the sister chromatids of the remaining chromosomes together break, and each sister chromatid is pulled apart from its partner. Cytokinesis then occurs again, this time splitting the two cells created after meiosis I into four gametes (Diffen, 2012). Other differences between the two include crossing over during prophase of meiosis but not mitosis, the halving of chromosomes during meiosis but not mitosis, and the separation of homologous pairs of chromosomes that only occurs during anaphase I of meiosis I.
The third point for contrasting mitosis and meiosis is the functions they serve on the organismal level. Mitosis is used to further the growth of an organism, develop and produce new cells, and repair any damage to cells that may have cropped up. Producing identical cells during the process of mitosis ensures that these daughter cells will be able to carry out the same functions as the original cells, which is crucial for not only the growth of the organism but also for repair (Reese, 2015). WIthout mitosis, it is likely that no eukaryotic or multicellular organisms or multicellular organisms would exist on Earth. On the other hand, meiosis and the gametes that it produces are exclusively used for sexual reproduction in sexually reproducing organisms. It is for this reason that the chromosomal number must be halved during meiosis, because if not, the organism’s chromosomal number would increase with each generation and it would no longer be genetically suitable for life. Since meiosis is used for sexual reproduction, creating variation in the genetics of the species through crossing over and other events during meiosis is crucial. Genetic variety bolsters the chances that a species will be able to survive in and adapt to the environment it is a part of and then successfully reproduce and pass these helpful traits onto its offspring (Reese, 2015). Although they have different purposes within cells, mitosis and meiosis are equally important for life.
Mitosis and meiosis are clearly shown to be two of the most important process for life, from how mitosis contributes to the development and growth of an organism and how meiosis ensures the continued survival of a species. Although there has not been a real consensus made for which process is more important to the continued survival of complex life forms on this planet, mitosis is clearly more crucial. Without mitosis, cells could not be replaced or repaired when they were damaged, meaning that the survival of an organism in an often hostile environment would be impossible. Mitosis is the only process that can allow an organism to grow past a unicellular stage, meaning that complex life would not be able to exist on Earth if it did not take place. In addition, mitosis allows for the exact copying of each chromosome to all of the daughter cells, keeping the organism’s DNA viable long before fertilization or meiosis would even occur. Overall, even with numerous differences in function, purpose, and results, mitosis and meiosis continue to work together to make life on Earth sustainable to this day.
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