Compare and contrast mitosis and meiosis which of the following statements are false

Mitosis and meiosis share some similarities, but also some differences, most of which are observed during meiosis I.

Learning Objectives

• Compare and contrast mitosis and meiosis

Mitosis and meiosis are both forms of division of the nucleus in eukaryotic cells. They share some similarities, but also exhibit distinct differences that lead to very different outcomes. The purpose of mitosis is cell regeneration, growth, and asexual reproduction,while the purpose of meiosis is the production of gametes for sexual reproduction. Mitosis is a single nuclear division that results in two nuclei that are usually partitioned into two new daughter cells. The nuclei resulting from a mitotic division are genetically identical to the original nucleus. They have the same number of sets of chromosomes, one set in the case of haploid cells and two sets in the case of diploid cells. In most plants and all animal species, it is typically diploid cells that undergo mitosis to form new diploid cells. In contrast, meiosis consists of two nuclear divisions resulting in four nuclei that are usually partitioned into four new haploid daughter cells. The nuclei resulting from meiosis are not genetically identical and they contain one chromosome set only. This is half the number of chromosome sets in the original cell, which is diploid.

Comparing Meiosis and Mitosis: Meiosis and mitosis are both preceded by one round of DNA replication; however, meiosis includes two nuclear divisions. The four daughter cells resulting from meiosis are haploid and genetically distinct. The daughter cells resulting from mitosis are diploid and identical to the parent cell.

The main differences between mitosis and meiosis occur in meiosis I. In meiosis I, the homologous chromosome pairs become associated with each other and are bound together with the synaptonemal complex. Chiasmata develop and crossover occurs between homologous chromosomes, which then line up along the metaphase plate in tetrads with kinetochore fibers from opposite spindle poles attached to each kinetochore of a homolog in a tetrad. All of these events occur only in meiosis I.

When the tetrad is broken up and the homologous chromosomes move to opposite poles, the ploidy level is reduced from two to one. For this reason, meiosis I is referred to as a reduction division. There is no such reduction in ploidy level during mitosis.

Meiosis II is much more similar to a mitotic division. In this case, the duplicated chromosomes (only one set, as the homologous pairs have now been separated into two different cells) line up on the metaphase plate with divided kinetochores attached to kinetochore fibers from opposite poles. During anaphase II and mitotic anaphase, the kinetochores divide and sister chromatids, now referred to as chromosomes, are pulled to opposite poles. The two daughter cells of mitosis, however, are identical, unlike the daughter cells produced by meiosis. They are different because there has been at least one crossover per chromosome. Meiosis II is not a reduction division because, although there are fewer copies of the genome in the resulting cells, there is still one set of chromosomes, as there was at the end of meiosis I. Meiosis II is, therefore, referred to as equatorial division.

Mitosis and meiosis are both processes by which cells reproduce, but there are distinct differences between the two. While new cells are generated during mitosis, meiosis is a special type of cell division that produces sex cells for reproduction. The two processes were discovered by different scientists. Meiosis was discovered by German biologist Oscar Hertwig while German physician Walther Flemming is credited with the discovery of mitosis.

The Purpose of the Reproduction

Only sexually reproductive organisms utilize meiosis. The role of the process is to produce sex cells and to repair genetic defects in germ line cells (the sex cells).

Both sexual and asexual organisms go through the process of mitosis. It happens in the cells of the body known as the somatic cells and produces cells related to growth and repair. Mitosis is essential for asexual reproduction, regeneration, and growth. It does not make sex cells or gametes.

Number of Daughter Cells

In meiosis, four haploid cells containing half the amount of chromosomes are produced at the end of the process.

Alternatively, two diploid cells, containing two sets of chromosomes, are produced as a result of mitosis.

Composition of the Daughter Cells

The daughter cells produced at the end of meiosis are completely different from the original parent cell and they include a mix of both the maternal and paternal genes, leading to genetic diversity during sexual reproduction.

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The daughter cells created in mitosis are genetically the same as the original parent cell.

Meiosis has two phases for the reproduction of cells which results in there being two cell divisions. The first phase includes prophase I  - during which the most important events of meiosis occur, metaphase I, anaphase I, telophase I, and cytokinesis. During the second phase, these processes repeat again with the cells that were formed at the end of the first phase.

In mitosis, the cells divide only once and this is via one phase which includes steps such as prophase, prometaphase, metaphase, anaphase, telophase and cytokinesis.

Pairing of Homologues

Meiosis involves the pairing of homologues, chromosomes similar to other chromosomes, whereas mitosis involves no pairing of homologues.

Differences in Anaphase

During the anaphase of meiosis, the sister chromatids do not separate. In anaphase I, the chromosomes are double-stranded and in Anaphase II, they are single stranded.

During anaphase in mitosis, the sister chromatids do separate at the centromeres and the chromosomes are single stranded.

Differences in Telophase

In mitosis, the spindle fibres recede fully during telophase, but this is not the case with telophase I of meiosis. Also the nucleoli reappear in mitosis but not in meiosis.

Mixing of Chromosomes

In meiosis, the chromosomes cross over causing mixing. Mitosis, on the other hand, does not involve crossing over of the chromosomes.

References

Further Reading

• All Meiosis Content
• Meiosis Process

Last updated Feb 26, 2019