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Mitosis and Meiosis

Written by tutor Mindi D.

Mitosis

What is Mitosis? Mitosis is the division of a eukaryotic cell’s nucleus leading to cytokinesis, which ultimately results in two identical cells (called daughter cells). The Mitotic phase is short part of the overall cell cycle – which contains Interphase. As a quick review, interphase has 3 phases: G1, S and G2 – during these steps leading up to the Mitotic phase, the cell grows and chromosomes are replicated. If all goes well during interphase the cell will progress into Mitotic Phase (‘mitosis”). There are 5 distinct phases of mitosis: Prophase, Metaphase, Anaphase, Telophase and Cytokinesis. The end result in Mitosis is 2 diploid cells. Let’s take a closer look as to what happens during each phase individually:

Prophase:

At the start of Prophase, chromatin, which is a loose bundle of genetic material, begins to become more tightly coiled together. The nucleous also disappears or disintegrates. The mitotic spindle is formed as well.

Metaphase:

The chromosome line up in the middle of the cell along an “imaginary line” called the metaphase plate with the help of the spindle fibers.

Anaphase:

The pair chromosomes separate and begin to move to opposite sides of the cells.

Telophase:

The spilt chromosome (called a chromatid) is now at the opposite pole. A new membrane forms around the new nuclei (the daughter nuclei).

Cytokinesis:

This is the step were the two daughter cells split apart and are separate; each daughter cell has its own membrane and nucleus.

Meiosis

What is Meiosis and how does it differ from Mitosis? Meiosis is also a form of cell division, but is unique because it is necessary for sexual reproduction in animal (eukaryotic) cells. The final resultant in Meiosis is called a gamete (or sex cell – egg and sperm). The cell from meiosis is haploid. The other unique aspect that make meiosis different is that you get genetic diversity (in mitosis all the cells are the same). There are 2 phases in meiosis that are further broken down... Let’s look at each step:

Prophase I:

At the start of Prophase I, DNA is replicated. Bivalents (aka paired chromosomes) are present.

Metaphase I:

Similar to Metaphase in mitosis, the two chromosomes (bivalents) line up on an imaginary equator called the metaphase plate.

Anaphase I:

The two pairs of chromosomes separate and a chromosome containing two chromatids moves towards its respective poles. At this point each daughter cell contains only 23 chromosomes making it haploid.

Telophase I:

A nuclear envelope forms OR the cell enters directing into meiosis II.

Prophase II, Metaphase II, Anaphase II, Telophase II and Cytokinesis

These processes follow the pattern of Meiosis I with an end result of 4 completely separate haploid daughter cells.

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