Which of the following occur in both mitosis and meiosis? select all that apply.

Cell division occurs as a part of the “cell cycle”. Just like your day has a routine from day to night, cells have routines of their own. The cell cycle is generally described as consisting of four main phases: G1, S phase, G2 and mitosis (or meiosis). Cells can also take a break from the grind of the cell cycle, in a state called G0 or senescence (note that some cells are permanently in G0). External growth factors can stimulate cells in G1 or G0 to proceed through the rest of the cycle, an example is Nerve Growth Factor (NGF), which promotes neuron growth. The restriction point is a special “point of no return” in G1 when cells no longer respond to removal of growth factors and will continue to progress to S phase no matter what. There are also internal signals that tell the cell to progress, these proteins are called cyclins and the cyclin that promotes mitosis is called cyclin B. S phase is especially important as this is the point at which the cell’s entire genome is duplicated through the process of semi-conservative DNA replication.

The stages of mitosis are interphase, prophase, metaphase, anaphase and telophase, sometimes followed by cytokinesis. “Interphase” is a blanket term which describes all the stages before mitosis, that is: G1, S and G2 phases. The stages of meiosis are interphase, prophase I, metaphase I, anaphase I, telophase I, cytokinesis I, prophase II, metaphase II, anaphase II, telophase II, and finally cytokinesis II. See our detailed explanation below:

Another way to understand the progression of mitosis and meiosis is by thinking about what is happeningto the chromosomes, centrosomes, nuclear membrane and cell plasma membrane at each stage of the process. Here we show how to do this for mitosis, why not try to recreate this table for meiosis?

Mnemonics are also helpful, for example a useful mnemonic to remember the order of the steps in mitosis is “I Prefer Mating At Teatime” – Chamillionaire.

The process of cell division is an intricate dance of molecular machinery that has fascinated researchers for hundreds of years. Advances in microscopy have had a huge impact on the field, from its humble beginnings observing metaphase chromosomes under the light microscope, to more sophisticated technologies today that can ask questions at the molecular level. Research into the cell cycle has also been highly rewarded, with the 2001 Nobel Prize in Physiology/Medicine being awarded to Tim Hunt, Paul Nurse and Leland Hartwell for their joint discovery of cyclins and cyclin-dependent kinases: the key regulators of the cell cycle [6]. However, despite our progress, many questions still remain.

While there is only one way for mitosis to go right, there are many ways for it to go wrong. For example, in early mitosis, if there are incorrect contacts between microtubules and chromosomes, chromosomes can become misaligned, which can lead to incorrect segregation of sister chromatids. In late mitosis, how is the cell certain that the time is right to perform cytokinesis? The chromosome passenger complex (CPC) is a molecular guardian angel that acts at many stages of mitosis to safeguard the fidelity of the process. At the start of mitosis, the CPC localises all over the chromosomes and acts to modify chromatin, during mitosis it moves to the chromosome centromeres to prevent incorrect microtubule attachments and before cytokinesis the CPC finds its way to the central spindle. Therefore, a question of ongoing research is how does the CPC elegantly re-localise throughout mitosis to save the day?

•Vader, G., Medema, R. H., & Lens, S. M. (2006). The chromosomal passenger complex: guiding Aurora-B through mitosis. The Journal of cell biology, 173(6), 833-837.

•Kabeche, L., Nguyen, H. D., Buisson, R., & Zou, L. (2018). A mitosis-specific and R loop–driven ATR pathway promotes faithful chromosome segregation. Science, 359(6371), 108-114.

You might remember from above that it is the protein cohesin that holds together sister chromatids in metaphase of mitosis and metaphase II of meiosis. However, in meiosis I homologous chromosomes must be held together in metaphase I, before these ties are swiftly broken during anaphase I. This feat is performed by a miraculous cellular zipper called the synaptonemal complex (SC). This zipper must be strong enough to hold chromosomes together, but it must also be disassembled equally efficiently, otherwise homologous chromosomes will not accurately segregate in anaphase I, leading to a potentially disastrous genetic inequality in the daughter cells. How exactly this zipper disassembles is a hot topic of research.

•Argunhan, B., Tsubouchi, T., & Tsubouchi, H. (2018). Polo is not solo in meiosis. Cell Cycle, 17(3), 273-274.

•Gao, J., & Colaiácovo, M. P. (2017). Zipping and unzipping: protein modifications regulating synaptonemal complex dynamics. Trends in Genetics.

References

1)Bennett, M. D. (1977). The time and duration of meiosis. Phil. Trans. R. Soc. Lond. B, 277(955), 201-226.

2)Jett, J. H. (2015). How long does it take a cell to divide? Cytometry Part A, 87(5), 383-384.

3)Brewer, B. J., Chlebowicz-Sledziewska, E., & Fangman, W. L. (1984). Cell cycle phases in the unequal mother/daughter cell cycles of Saccharomyces cerevisiae. Molecular and cellular biology, 4(11), 2529-2531.

4)Clift, D., & Schuh, M. (2013). Restarting life: fertilization and the transition from meiosis to mitosis. Nature reviews Molecular cell biology, 14(9), 549.

5)Paweletz, N. (2001). Walther Flemming: pioneer of mitosis research. Nature Reviews Molecular Cell Biology, 2(1), 72.

6)Nurse, P. M. (2002). Nobel Lecture: Cyclin dependent kinases and cell cycle control. Bioscience reports, 22(5), 487-499.

Organisms grow and reproduce through cell division. In eukaryotic cells, the production of new cells occurs as a result of mitosis and meiosis. These two nuclear division processes are similar but distinct. Both processes involve the division of a diploid cell, or a cell containing two sets of chromosomes (one chromosome donated from each parent).

In mitosis, the genetic material (DNA) in a cell is duplicated and divided equally between two cells. The dividing cell goes through an ordered series of events called the cell cycle. The mitotic cell cycle is initiated by the presence of certain growth factors or other signals that indicate that the production of new cells is needed. Somatic cells of the body replicate by mitosis. Examples of somatic cells include fat cells, blood cells, skin cells, or any body cell that is not a sex cell. Mitosis is necessary to replace dead cells, damaged cells, or cells that have short life spans.

Meiosis is the process by which gametes (sex cells) are generated in organisms that reproduce sexually. Gametes are produced in male and female gonads and contain one-half the number of chromosomes as the original cell. New gene combinations are introduced in a population through the genetic recombination that occurs during meiosis. Thus, unlike the two genetically identical cells produced in mitosis, the meiotic cell cycle produces four cells that are genetically different.

• Mitosis and meiosis are nuclear division processes that occur during cell division.
• Mitosis involves the division of body cells, while meiosis involves the division of sex cells.
• The division of a cell occurs once in mitosis but twice in meiosis.
• Two daughter cells are produced after mitosis and cytoplasmic division, while four daughter cells are produced after meiosis.
• Daughter cells resulting from mitosis are diploid, while those resulting from meiosis are haploid.
• Daughter cells that are the product of mitosis are genetically identical. Daughter cells produced after meiosis are genetically diverse.
• Tetrad formation occurs in meiosis but not mitosis.

1. Cell Division

2. Daughter Cell Number

• Mitosis: Two daughter cells are produced. Each cell is diploid containing the same number of chromosomes.
• Meiosis: Four daughter cells are produced. Each cell is haploid containing one-half the number of chromosomes as the original cell.

3. Genetic Composition

• Mitosis: The resulting daughter cells in mitosis are genetic clones (they are genetically identical). No recombination or crossing over occur.
• Meiosis: The resulting daughter cells contain different combinations of genes. Genetic recombination occurs as a result of the random segregation of homologous chromosomes into different cells and by the process of crossing over (transfer of genes between homologous chromosomes).

4. Length of Prophase

• Mitosis: During the first mitotic stage, known as prophase, chromatin condenses into discrete chromosomes, the nuclear envelope breaks down, and spindle fibers form at opposite poles of the cell. A cell spends less time in prophase of mitosis than a cell in prophase I of meiosis.
• Meiosis: Prophase I consists of five stages and lasts longer than prophase of mitosis. The five stages of meiotic prophase I are leptotene, zygotene, pachytene, diplotene, and diakinesis. These five stages do not occur in mitosis. Genetic recombination and crossing over take place during prophase I.

5. Tetrad Formation

• Mitosis: Tetrad formation does not occur.
• Meiosis: In prophase I, pairs of homologous chromosomes line up closely together forming what is called a tetrad. A tetrad consists of four chromatids (two sets of sister chromatids).

6. Chromosome Alignment in Metaphase

• Mitosis: Sister chromatids (duplicated chromosome comprised of two identical chromosomes connected at the centromere region) align at the metaphase plate (a plane that is equally distant from the two cell poles).
• Meiosis: Tetrads (homologous chromosome pairs) align at the metaphase plate in metaphase I.

7. Chromosome Separation

• Mitosis: During anaphase, sister chromatids separate and begin migrating centromere first toward opposite poles of the cell. A separated sister chromatid becomes known as daughter chromosome and is considered a full chromosome.
• Meiosis: Homologous chromosomes migrate toward opposite poles of the cell during anaphase I. Sister chromatids do not separate in anaphase I.

While the processes of mitosis and meiosis contain a number of differences, they are also similar in many ways. Both processes have a growth period called interphase, in which a cell replicates its genetic material and organelles in preparation for division.

Both mitosis and meiosis involve phases: Prophase, Metaphase, Anaphase and Telophase. Although in meiosis, a cell goes through these cell cycle phases twice. Both processes also involve the lining up of individual duplicated chromosomes, known as sister chromatids, along the metaphase plate. This happens in metaphase of mitosis and metaphase II of meiosis.

In addition, both mitosis and meiosis involve the separation of sister chromatids and the formation of daughter chromosomes. This event occurs in anaphase of mitosis and anaphase II of meiosis. Finally, both processes end with the division of the cytoplasm that produces individual cells.