Metaphase: What is it? Function in Mitosis, Function in Meiosis and Division Phases

It is the second phase of mitosis (cell division), where the nuclear membrane disappears and the chromosomes are located in the equatorial plane of the cell.

It is a stage in the division of eukaryotic cells in which the chromosomes are aligned in the metaphase plate in the middle of the cell. The stages of prophase and prometaphase come before the metaphase. In those stages of cell division, chromosomes condense, spindle fibers are formed and the nuclear envelope decomposes.

During the metaphase and the prometaphase late, the cell behaves like a series of control points to ensure that the axis has been formed.

The microtubules emanating from each side of the cell bind to each chromosome. As the microtubules retract, an equal voltage is applied from each side of the cell to the chromosomes.

This moves them to the center of the cell. After the metaphase, the sister chromatids that make up the chromosomes are divided and the process of cell division is completed.

At the beginning of the eukaryotic cell division, the centriole divides and begins to establish the network of microtubules that will move the chromosomes and organelles along the process of cell division. These microtubules coil to form larger fibers, which extend from the centrosomes.

Although the fibers are stable near the centrosomes, as they extend into the chromosomes, they are less stable.

As the fibers grow toward the chromosome, both add and subtract pieces at the unstable end. As the fibers grow in this way, 3 steps forward 2 steps back, wander through the cytoplasm .

Finally, the fibers connect to the centromere of a chromosome. Each centromere has a kinetochore where the microtubules can be joined.

The most important process that takes place before and during the metaphase is the control point of the shaft assembly. The control point of the axis assembly is a complex series of mechanisms that ensures the proper division of the chromosomes.

Although chromosomes align differently during mitosis and meiosis, both pass through a spindle assembly checkpoint during the metaphase.

If these control points are omitted, or not functioning correctly, the cell will start anaphase before the chromosomes properly attach to the microtubules and line up on the metaphase plate.

If this is the case, the chromosomes are classified in the wrong cells. This can produce too many or too few chromosomes in the resulting daughter cells. In meiosis, this can lead to birth defects and non-viable offspring. If it occurs during mitosis, this can cause the cells to become cancerous.

Metafase en Mitosis

During mitosis, the chromosomes are aligned in the center of the cell, with the sister chromatids of each chromosome on each side of the metaphase plate. Before mitosis, during the interphase, the cell replicates its DNA.

The chromosomes that contain the DNA are condensed before, so they will not be damaged by the movements that will take place during the metaphase.

At the beginning of the metaphase, and during the late prometaphase, the chromosomes are randomly organized within the nucleus. The nuclear membrane dissolves and the microtubules connect to each chromosome.

In mitosis, the microtubules of each centrosome are connected to each chromosome. Chromosomes consist of two sister chromatids, which are connected by proteins called cohesins.

Before the cohesins can be broken, the mitotic spindle control point must be met, which means that all the chromosomes are attached to the microtubules on both sides and are aligned on the metaphase plate.

When this control point is passed, the chromosomes emit a signal that activates the anaphase promoter complex. Activation of this complex leads to the end of the metaphase in mitosis and to the onset of anaphase.

The alignment of the chromosomes, with sister chromatids on each side of the metaphase plate, ensures that the two new cells will be identical. The sister chromatids represent the two new DNA strands created from a chromosome during the stage of synthesis of the interface.

By separating all these copies into new cells, the two new cells created are identical to the initial cell. Mitosis is used in this way to develop new organisms and repair damaged tissues.

As will be seen in meiosis, the chromosomes are aligned differently and the cell divides twice, resulting in a reduction of the genetic material in each cell.

Metafase en meiosis

Division phases:

Metaphase I:  During the first division of meiosis, meiosis I, the homologous chromosomes are divided into a cell. As in mitosis, DNA has replicated before meiosis, and all chromosomes exist as sister chromatids.

Each chromosome has a homologous pair, which represents the same portion of DNA but with different alleles .

Unlike mitosis, these homologous pairs are linked together through metaphase I of meiosis. Instead of sister chromatids that are aligned in the metaphase plate, in metaphase I the homologous pairs are aligned in the metaphase plate.

A spindle control point, this so-called meiotic spindle control point, must still be passed. If all the chromosomes are attached to their homologous pair, and each pair is bound to the microtubules on each side, the cell can go on to anaphase I. During anaphase I, the homologous pairs will separate.

Therefore, the ploidy of the cells will be reduced to diploid haploid because each new cell will have a single copy of the genome, or only one allele per gene. Mishaps during metaphase They can cause cells to have an incorrect number of each chromosome in each cell.

If even a homologous pair does not separate well, the resulting gametes can produce non-viable offspring. If metaphase I is successful, meiosis I can continue, creating two cells, each with two copies of half full genome.

Metaphase II:  After a brief rest called interkinesis, the cells will begin to divide again.

DNA replication does not occur during this interruption, therefore, each cell has two copies of one allele for each gene. The chromosomes condense again in prophase II and the nuclear envelope decomposes at the beginning of metaphase II.

This time, however, there are no homologous pairs present, only sister chromatids.

During metaphase II, these chromosomes will be aligned in the metaphase plate through the same processes described above. As in mitosis, the sister chromatids will break once the control point of the meiotic spindle has passed.

The cells can continue their division until 4 cells are produced in total. These cells will each have only one allele per gene, and only one copy of each allele.