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Meiosis - Dual Cell Division



Meiosis phases

Introduction

Contrary to what happens in mitosis (where there is only one cell division), in meiosis two cells divide at the same time.

How it happens (summary)

The phases of this process (prophase, metaphase, anaphase, telophase, interphase) occur in the same way as in mitosis; only, in this case, double, because here we will have two cells going through the same process simultaneously.

In meiosis, four new cells will be created from two cells. Each of these new cells will carry half the DNA of its original cell.

Meiosis begins when the organism is in the reproduction phase. The phases of meiosis cell division are easy to understand for those who understand the process of mitosis.

While in mitosis only one cell goes through the stages of division (prophase, metaphase, anaphase, telophase, interphase) to generate two daughter cells, in meiosis the same will occur, but in this case two cells will go through this process at the same time to generate four daughter cells.

To identify each cell's steps during meiosis, there is a scientific definition known as Meiosis I and Meiosis II. More simply, we can understand that this is nothing more than two cells simultaneously going through the "same" steps that occur in mitosis.

In meiosis, the phase of interphase (when cells are not dividing) is quite short and there is no duplication of DNA.

As explained earlier, meiosis begins when the cell is in the reproduction phase. From this moment on, there will be a mixture of genes between the two cells. It is important to know that this process is quite common among living organisms like plants, animals, and even some types of fungi.

Instead of creating two new cells with identical numbers of chromosomes (as in mitosis), in meiosis the cells make a second division (meiosis II) right after the first (meiosis I).

In this second division the number of chromosomes is divided in half. At only half the number of chromosomes, cells are called haploids. Diploid cells are just the opposite of haploid cells. Cells in their normal stage are considered diploid.

Meiosis steps

Meiosis I

Basically the meiosis phases are similar to that of mitosis. In both, the chromosome pairs align at the center of the cell and move to opposite sides. Meiosis differs by the crossing-over that occurs with DNA.

This crossing over is the exchange of genes between cells. In this exchange, the genes are mixed and the result of this exchange is not a perfect duplication as in mitosis. Here the cells divide into two new cells with just one pair of chromosomes each.

Because the interphase period is too short in meiosis, cells do not have time to duplicate their chromosomes to perform a mitotic division, so they again depart for a meiotic division, initiating meiosis II.

Meiosis II

In prophase II the remaining DNA in cells condenses into short chromosomes. Each pair of chromosomes has a centromere. The centrioles begin their journey to opposite sides of the cell.

Metaphase II: At this stage the chromosomes are already aligned in the center of the cell and the centrioles are ready for duplication.

Anaphase II: Here the chromosomes appear divided and move towards opposite sides of the cell. They do not divide DNA between new cells, instead they divide existing DNA. Each child cell will take only what is necessary for its metabolic functions.

Telophase II: At this stage the DNA has been completely pulled aside. At the end of this phase, there will be four haploid cells that are called gametes. The goal of gametes is to find other gametes to then combine and become a new organism.

Note: meiosis occurs only in male and female germ cells.