Metaphase In Mitosis And Meiosis (Metaphase 1 And 2)

Metaphase In Mitosis And Meiosis Overview

Metaphase Definition

The cell cycle stage known as metaphase is present throughout both the mitotic and meiotic division processes. During metaphase in mitosis and meiosis, the chromosomes condense and become prominent and viewable during alignment in the centre of the dividing cell, forming a metaphase plate at the middle of the cell.

During this phase, many tests are conducted to ensure that the spindles are manufactured. The metaphase stage is utilised in karyotyping tests to find chromosomal abnormalities.

What happens in metaphase?

  • During metaphase, the genetic material that is duplicated in the nucleus of the parent cells is separated, resulting in the formation of two daughter cells that are exactly alike.
  • The alignment of the chromosomes in the cell’s core is accomplished during metaphase by a process that some could refer to as a cellular tug of war.
  • The sister chromatids of the duplicated chromosomes continue to be connected at the centromere.
  • The prophase stage creates radial microtubules surrounding the centrosome called kinetochores prior to metaphase.
  • Kinetochore microtubules, which protrude from the poles at each end of the cell, are long protein filament microtubules that hold the kinetochores in place.
  • The kinetochore tubules move the sister chromatids back and forth (tug of war) till they align at the cell’s equator. A plane equatorial to this is created.
  • Additionally, during metaphase, a metaphase checkpoint also occurs.
  • By examining the chromosomal alignment and the proper attachment of the kinetochores, the metaphase checkpoint, sometimes referred to as the spindle assembly checkpoint, verifies that the cell is ready to divide.
  • Despite the chromosomal alignment discrepancies between mitosis and meiosis, both kinds of cell cycles require the spindle assembly checkpoint to occur during metaphase.
  • The cell reaches the fourth stage of mitosis, known as the anaphase, when these procedures are successful.
  • After the chromosomes have condensed in prophase, the cell division cycle continues with the phase known as metaphase.
  • Condensation plays a crucial role in protecting the chromosomes (chromatids) from harm during metaphase’s pulling and pushing forces.
  • The chromosomes are observed to be disorderly organised within the cell nucleus and within a fragmented nuclear membrane at the conclusion of prophase or prometaphase.
  • The polar and radial microtubules are nevertheless joined to every chromosome.
  • Each chromosome, which consists of two identical sister chromatids, is connected to the other chromosomes during mitosis by microtubules from each centrosome. Cohesins are proteins that bind the sister chromatids together.
  • Because they exert the forces of pulling and pushing, microtubules enable the cell to be a dynamic entity.
  • The sister chromatids are able to align in the cell’s centre to create a metaphase plate thanks to the kinetochore microtubules.
  • Tubulin, a microtubule component, is continuously added to and withdrawn from the ends of the microtubules. As a result, the sister chromatids and microtubules travel in a treadmill-like manner.
  • The sister chromatids are tightly held together by these treadmilling forces.
  • Thanks to the alignment of the chromatids along the metaphase plate, the newly formed cells will be similar.
  • The spindle assembly checkpoint can only occur when the chromatids are aligned at the metaphase plate and connected to the microtubules from both poles of the cell.
  • The chromosomal alignment process known as metaphase, which can last days, is extended by the checkpoint.
  • Following the checkpoint, a signal from the chromosomes activates the anaphase-promoting complex, bringing on the end of metaphase and the start of anaphase.

Metaphase of Meiosis

Metaphase I in Meiosis

  • A diploid cell divides into a haploid during meiosis I. The cells involved are comparable (half of the chromosomes).
  • Chromosome crossing over genes, which results in genetic variation in the daughter cells of the subsequent generation from the parent cells, is the mechanism by which it operates.
  • Before meiosis, DNA replication creates sister chromatids; as a result, during meiosis I, the procedure begins with a pair of identical chromosomes.
  • Despite the fact that the homologous pair represents identical DNA, it includes unique alleles.
  • In contrast to mitosis, sister chromatids align on the metaphase plate during metaphase. During metaphase, the homologous pairs will adhere to one another and proceed through the alignment.
  • At this time, a spindle checkpoint, often called the meiotic spindle checkpoint, occurs.
  • Before proceeding to the subsequent phase, anaphase I, this checkpoint ensures that the homologous pairs and every pair are connected to the kinetochore microtubules on both sides of the cell.
  • The continuation of meiosis After a successful metaphase, I guarantee the production of two cells, each with two copies of half of the whole genome.

Metaphase II in Meiosis

  • This is meiosis II’s second phase.
  • Currently, the meiotic spindles of the two daughter cells produced by the initial meiotic division are beginning to drag the chromosomes back to the metaphase plate.
  • This prepares the centrosome for division in the subsequent step.
  • After a brief interlude known as interkinesis, it occurs.
  • As a result, the cells begin to divide once more without any DNA replication happening. As a result, each gene will have two copies in each cell of each allele.
  • Additionally, once metaphase II starts, the nuclear envelope degrades.
  • At this moment, the two kinetochores of every centromere will join the spindle fibres from the opposite poles.
  • In the following step, this causes the sister chromatids of each chromosome to separate.
  • The isolation of the chromatids, which allows for a quick transition to the following phase, also triggers a meiotic spindle checkpoint.

Applications of Metaphase

Karyotyping can be used to identify genetic abnormalities during the metaphase stage of cell division.

This is due to the fact that cross-overs (meiosis) occur during this phase, Moreover, if the mitotic spindle checkpoint and the meiotic spindle checkpoint are skipped, the chromatids may be injured by the pulling and pushing of the kinetochore microtubules.

References and Sources

  • https://www.sparknotes.com/biology/cellreproduction/mitosis/section2/
  • https://www.britannica.com/science/metaphase
  • https://www.sciencedirect.com/topics/biochemistry-genetics-and-molecular-biology/metaphase
  • https://www.genome.gov/genetics-glossary/Metaphase
  • https://www.nature.com/scitable/definition/metaphase-249/
  • https://www.nature.com/scitable/topicpage/mitosis-and-cell-division-205/
  • http://www.phschool.com/science/biology_place/biocoach/meiosis/metai.html#:~:text=The%20centrioles%20are%20at%20opposite,poles%20called%20the%20metaphase%20plate.
  • https://www.sciencedirect.com/science/article/abs/pii/S0074769601120073
  • https://www.biologyonline.com/dictionary/metaphase-ii
  • http://cyberbridge.mcb.harvard.edu/mitosis_6.html
  • http://cyberbridge.mcb.harvard.edu/mitosis_7.html
  • http://www.macroevolution.net/metaphase-ii.html
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