Phases+&+Cytokinesis

//*Unlike in mitosis, all phases during Meiosis II occur simultaneously in both two daughter cells produced in Meiosis I This being the exception in egg production in females).//

__Mitosis__ Mitosis consists of five phases: Interphase, Prophase, Metaphase, Anaphase, and Telophase. Within Interphase there are three sub-phases known as Gap 1, DNA Synthesis, and Gap 2. Cell division occurs only once
 * Number**

__Meiosis__ Generally it is known that meiosis has nine phases in total: Interphase, Prophase I & II, Metaphase I & II, Anaphase I & II, and Telophase I & II. However some of these phases may be excluded in different species of organisms; in some species, an additional phase called Interkinesis is included or Telophase I and II are excluded. Cell division occurs twice in meiosis unlike mitosis.

__Mitosis__ In Interphase of mitosis there are three sub-phases: Gap 1, DNA Synthesis, and Gap 2. During Gap 1 and Gap the cell goes through “check-ups” determining if the cell is prepared to divide; does the cell have adequate number of organelles and nutrients? Is it large enough (in size)? Is the DNA relatively undamaged? During DNA Synthesis DNA is duplicated, and there are in total two full sets of DNA. During Gap 1 through Gap 2, the cell also continues to grow in size.
 * Interphase

__Meiosis__ Interphase I of meiosis same as mitosis Interphase in function. The second short Interphase of meiosis also known as Interkinesis, a phase present in some species is different from mitosis’s Interphase; it is shorter in duration, and DNA duplication (DNA Synthesis) does not take place.

****Prophase** __Mitosis__ In mitosis during Prophase, chromatin condenses into tightly coiled chromosomes. The nuclear membrane and the nucleolus break down. As each centrosome that has been duplicated during Interphase move toward the opposite poles of the cell a type of microtubule called spindle fiber emanates.

__Meiosis__ Like in Prophase of mitosis, chromatin condense into chromosomes visible under the light microscope, nuclear membrane and the nucleolus break down, and centrosomes move toward each ends of the cell, forming spindle fibers (also known as mitotic fibers) during Prophase I and II. However in these phases unlike in mitosis Prophase the homologues (some from mother, and others from father) go through Synapsis or pairing of homologues along same types of genes. Once the homologues (one that maternally-driven, and another one that is paternally-driven) have paired up, crossing over may occur (exchange of genes).

__Mitosis__ During Metaphase in mitosis, the spindle fibers emanating from centrosomes located in opposite poles of the cell attach to kinetochores in the centromeres of the chromosomes. Spindle fibers forming from both centrosomes attach to a common centromere of each chromosome. As the spindle fibers attach to the centromeres of the chromosomes, the chromosomes line up along the metaphase plate (also called equatorial plate).
 * Metaphase

__Meiosis__ Metaphase II of meiosis is identical in its process to Metaphase of mitosis; the chromosomes that have been altered in its genetic information in the past phases are attached to the spindle fibers from the centrosomes, and lined up in the metaphase plate. However, Metaphase I is considerably different from mitosis’ metaphase. In Metaphase I of meiosis, the spindle fibers projecting from opposite centrosomes attach only to their adjacent chromosomes’ external sides of the centromeres. The most prominent difference between meiosis’ Metaphase I and mitosis’ Metaphase lies in the processes that create genetic diversity. During Metaphase I, homologous pairs are randomly oriented (by “randomly oriented” meaning the maternal and paternally driven homologues are arrange in random sides) along the equatorial plate. Also crossing over occurs when enzymes “cut” sequences of DNA from each homologue of a pair and exchange these sequences between the homologues.

****Anaphase** __Mitosis__ During mitosis’ Anaphase, the sister chromatids are pulled apart toward the opposite poles of the cell as the spindle fibers shorten. Cytokinesis may begin towards the end of Anaphase.

__Meiosis__ In Anaphase II is equivalent in process to Anaphase of mitosis; the sister chromatids are pulled away. However, in Anaphase I, each homologue (or chromosome) of the homologous pair is pulled away towards opposite poles as the spindle fibers shorten. Cytokinesis may or may not begin during the end of Anaphase I and II depending on the species.

**Telophase**** __Mitosis__ Each full set of chromosomes is located at the opposite ends of the cell by the time Telophase begins. The spindle fibers detach from the centromeres of the chromosomes, and break down. Then, the nuclear envelope and nucleolus reform, and the chromosomes decondense into chromatins in each separate set. As Cytokinesis happens simultaneously, the cytoplasm is divided equally, and two daughter diploid cells form.

__Meiosis__ Telophase I and II of meiosis are equivalent to Telophase of mitosis in their fundamental processes. However, the difference is in the number of chromosomes in each cells resulting. In Telophase I, there are full set of chromosomes in each cell (diploid), and in Telophase II, there are half of the number of chromosomes usually present in a full chromosome set (haploid). Telophase I and/or II of meiosis may or may not occur depending on the species.

****Cytokinesis** //Division & Generation __Mitosis__ In mitosis’ Cytokinesis, cytoplasm is divided relatively equal between the two daughter cells. If the cytoplasm divides unequally and continues to do so in cells, it can cause two potential problems: the daughter cell with “less” cytoplasm may be too small for adequate number of organelles and molecules to be contained, and the daughter cell with “more” cytoplasm may be too big for molecules to be transported efficiently into, within, and out of the cell.

__Meiosis__ In Cytokinesis I and II of meiosis producing sperm cells, the cytoplasm like in mitosis is equally distributed (relatively). However Cytokinesis in meiosis yielding an egg is unequal in its division. During the first Cytokinesis of meiosis, the cytoplasm is unequally divided between two cells. The cell that has received more cytosol and organelles goes on to Meiosis II, while the cell with “less” cytoplasm (polar body) degenerates. Such is the case also in the second Cytokinesis of meiosis producing an egg; the daughter cell with “less” cytoplasm is degenerated, and the surviving cell with “more” cytoplasm goes through gametogenesis to fully become an egg.

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