Table of Contents
Metaphase may be a cell cycle stage that happens during both mitosis and meiosis cellular division. The chromosomes condense during metaphase in mitosis and meiosis, and they become visible and distinct during alignment at the centre of the dividing cell, forming a metaphase plate at the cell’s centre.
A set of checkpoints make sure that the spindles are produced during this era. The metaphase stage is utilised to detect chromosomal abnormalities in karyotyping tests.
What is Metaphase?
1. Metaphase is the process of separating the duplicated genetic material carried in the parent cells’ nuclei into two identical daughter cells.
2. During metaphase, the chromosomes at the cell’s core are aligned by pulling and pushing, a process that some refer to as a cellular tug of war.
3. The replicated chromosomes remain sister chromatids at the centromere.
4. Prior to metaphase, the prophase stage produced radial microtubules surrounding the centrosome known as kinetochores.
5. Long protein filament microtubules (kinetochore microtubules) that stretch from the poles on each end of the cell attach the kinetochores.
6. The sister chromatids are tugged back and forth by the kinetochore tubules until they are aligned at the cell’s equator. An equatorial plane is made as a results of this.
7. In addition, during metaphase, a metaphase checkpoint occurs.
8. The metaphase checkpoint, also known as the spindle assembly checkpoint, guarantees that the cell is ready to split by inspecting chromosomal alignment and kinetochores attachment.
9. Despite the chromosomal alignment variations between mitosis and meiosis, the spindle assembly checkpoint must occur during metaphase in both kinds of cell cycles.
10. The cell enters the fourth phase of mitosis, known as anaphase, when all of these steps are completed correctly.
Metaphase of Mitosis
1. Metaphase is a phase of the cell division cycle that occurs after the chromosomes have condensed during prophase.
2. The condensation process is necessary to guarantee that the chromosomes (chromatids) are not destroyed during the metaphase pulling and pushing pressures.
3. Chromosomes are randomly distributed within the cell nucleus, within a disintegrated nuclear membrane, near the conclusion of prophase or prometaphase.
4. However, each of the chromosomes is linked to the polar and radial microtubules.
5. Microtubules from each centrosome link to each chromosome, which is made up of two identical sister chromatids, during mitosis. Cohesins are proteins that link the sister chromatids.
6. The existence of microtubules permits the cell to be a dynamic entity by allowing pulling and pushing forces to be applied.
7. The kinetochore microtubules achieve this by allowing the sister chromatids to align at the cell’s centre, producing a metaphase plate.
8. The tubulin subunit of these microtubules is continually inserted and withdrawn from the microtubules’ ends. The microtubules and sister chromatids move during a treadmilling motion as a results of this.
9. The tight binding of the sister chromatids is aided by these treadmilling pressures.
10. The chromatid alignment along the metaphase plate guarantees that the new cells produced will be similar.
11. For the spindle assembly checkpoint to occur, the chromatids must be linked to the microtubules from both poles of the cell and aligned at the metaphase plate.
12. The checkpoint extends the metaphase period, which might last days if the chromosomes are correctly aligned.
13. After the checkpoint, the chromosomes release a signal that activates the anaphase-promoting complex, causing metaphase to finish and anaphase to begin.
Metaphase of Meiosis
Metaphase I of Meiosis
1. The cells engaged in meiosis I are similar in that a diploid cell splits into haploid cells (half of the chromosomes).
2. It operates by creating genetic variety in the daughter cells of the following generation of parent cells through chromosomal crossing over genes.
3. DNA replication occurs before meiosis, forming sister chromatids, and therefore the process begins with a homologous pair of each chromosome during meiosis I.
4. The homologous pair represents the same DNA but with distinct alleles.
5. Unlike mitosis, when the sister chromatids align on the metaphase plate, the homologous pairs will connect to each other during metaphase I and undergo alignment on the metaphase plate.
6. A spindle checkpoint, also known as the meiotic spindle checkpoint, occurs at this period.
7. Before moving on to the next phase, anaphase I, this checkpoint ensures that the homologous pairs and each pair are connected to the kinetochore microtubules from either side of the cell.
8. A fruitful Metaphase I ensures that meiosis continues to produce two cells, each with two copies of half of the genome.
Metaphase II in Meiosis
1. Meiosis II is now in its second phase.
2. During this phase, the meiotic spindles of the two daughter cells generated during the initial meiotic division begin to pull the chromosomes back to the metaphase plate.
3. This is to get the centrosome ready for the next step of division.
4. It occurs after a brief pause called as interkinesis.
5. This causes the cells to begin dividing again, but without any DNA replication. As a result, each cell will contain two copies of each gene’s allele.
6. As metaphase II begins, the nuclear envelope also begins to break down.
7. The two kinetochores of each centromere, on the other hand, will bind to the spindle fibres from opposing poles at this point.
8. In the following phase, the sister chromatids of each chromosome will be separated.
9. During the separation of the chromatids, a meiotic spindle checkpoint occurs, allowing for a quick transition to the next phase.
Application of Metaphase
1. Karyotyping is used to discover genetic abnormalities during the metaphase stage of cell division.
2. This is because cross overs (meiosis) occur during this phase, and the kinetochore microtubules’ pulling and pushing of the chromatids may induce chromosomal damage if the mitotic spindle checkpoint and the meiotic spindle checkpoint are missed.