Mitosis and Meiosis Compare and Contrast

Both mitosis and meiosis are processes of cell division that involve chromosome replication and division. However, they are different because mitosis produces cells that have the same ploidy as the parent cells but in meiosis, the ploidy of the resulting cells is halved. The products of mitosis are genetically identical diploid somatic cells but in meiosis, the resulting cells are genetically diverse in order to make sure that the offspring have different genetics from the parent cell.

Mitosis is the normal cellular process of the division of cells that happens during the entire life cycle of life. It allows for a multicellular adult to develop from a zygote and it leads to the production of cells for the growth and repairing of tissues. The production of two genetically identical daughter cells is ensured via mitosis. There are several stages of mitosis, including interphase, prophase, prometaphase, metaphase, anaphase, and telophase. In interphase, there are several steps, during the G1 phase the cell makes proteins required for DNA replication, during the S phase the replication of the chromosome occurs and is attached to the original chromosome by a centrome which yields a bivalent chromosome or two sister chromatids. During the G2 phase, the essential proteins for mitosis are produced. During prophase, the nuclear membrane goes away and the chromosomes condense and thicken, attaching themselves to microtubules that extend from the mitotic spindle fibres. In metaphase, the chromosomes line up along the cells' equator. The sister chromatids separate during anaphase and they start to move to opposite poles of the cell due to the contraction of the spindle fibres. The spindle fibres are not found in telophase, here the chromosomes decondensed, the nucleoli appear again and the nuclear membrane forms around each nucleus. The cell then splits into two cells in a process that is called cytokinesis which starts with the constriction of the cell that increases and eventually forms two daughter cells.

Meiosis is a more particular cell division process that forms haploid gametes, either an egg cell or a sperm cell that have half the amount of chromosomes that are present in the parent cell. Unlike mitosis, it is a reductive division and meiosis also has many functions. It has a narrow but very important process as it assists sexual reproduction. It is different to mitosis as in mitosis it leads to the production of two genetically identical daughter cells whereas in meiosis it is more complex and goes through additional phases to lead to the production of four genetically different haploid cells that have the potential to combine and become genetically diverse new diploid cells. The process of meiosis is split into meiosis I and meiosis II. Meiosis I is specific and unique to germ cells but meiosis II is similar to mitosis. Meiosis I starts with prophase 1 where the chromatin condenses to form chromosomes. The sister chromatids stay joined at the centromere and each pair of chromatids line up with their homologous pair and fasten together (known as synapsis) in a tread. In the tetrad, any pair of chromatid arms can overlap and fuse in a process called recombination producing a new combination of genes. In metaphase I the chromosomes line up a the equator attached by their centromeres to the spindle fibres which are still in their homologous pairs. During anaphase, I the fibres contract and separates the chromosomes, each with the two chromatids being at opposite poles. This is a contrast when compared to mitosis as chromosomes appear as individuals instead of as pairs. In telophase 1 it signifies the end of the first mitotic division and the cytoplasm cleaves to produce two new diploid cells. Each chromosome is copied and ready for the following meiotic division. In meiosis II occurs a mitotic division of each of the diploid cells that are made by meiosis I. During prophase II, the chromosomes condense and new spindle fibres are produced, the chromosomes move along the equator of the cell during metaphase II and the centromeres of the paired chromatids line up along the equator of both cells. In anaphase II the chromatids separate and the spindle fibres pull the separated chromosomes towards opposite poles. Lastly, during telophase II, the chromosomes decondensed and become enclosed by a nuclear membrane. This is followed by cytokinesis and divides the cells into four haploid sperm or egg cells. The result of meiosis II is four haploid cells made from one diploid cell. In males, four sperm cells are produced but in females, only one ovum is made as the other three cells become polar bodies and are disregarded and do not develop any further.

Overall there are several differences between mitosis and meiosis. In mitosis DNA replication happens during interphase and before cell division whereas in meiosis it occurs once during interphase before meiosis I. the number of divisions in mitosis happens once including prophase, metaphase, anaphase and telophase but in meiosis, there are two divisions including prophase, metaphase, anaphase and telophase. The synopsis of homologous chromosomes occurs during meiosis during prophase I and does not occur in mitosis, making it unique to meiosis. There are two genetically identical diploid daughter cells produced in mitosis but there are four haploid cells produced from meiosis which are half the ploidy and genetically different. Mitosis allows for multicellular adults to arise and allows for cell growth and tissue repair whereas meiosis aids in sexual reproduction and produces gametes with genetic variation.

07 July 2022
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