Definition of Metaphase
- Metaphase is a stage of the cell cycle that occurs in both mitosis and meiosis cell division. During this stage, individual chromosomes cannot be observed in the cell nucleus.
- The chromosomes during the metaphase are condensed and become distinguishable as they arrange in the middle of the dividing cell.
- The karyotyping procedure used the metaphase chromosomes to look for chromosomal abnormalities.
- In this stage, the nucleus get disappears and the chromosomes arrive in the cytoplasm of the cell.
- In human cells, the chromosomes then become visible under the microscope, during this stage.
- In medical research, the Cells of metaphase are used to estimate whether all of the chromosomes are present and whether or not they are all intact.
- The plane of alignment of the chromosomes at metaphase is referred to as the metaphase plate
- During Metaphase, the duplicated genetic materials are get separated which is carried within the nucleus of the parent cells, to form 2 same daughter cells.
- In this stage, the chromosomes are aligned at the center of the cell by pulling and pushing, and others would tern as a cellular tug of war.
- The replicated chromosomes get attached to the centromere as a form of sister chromatids.
- Before metaphase, the prophase stage occurs which helps in the formation of radial microtubules which are also known as kinetochores around the centrosome.
- A long protein filament microtubules known as kinetochore microtubules attach the kinetochores which is extend from the poles on either end of the cell.
- The kinetochore tubules pull back and forth (tug of war) the sister chromatids till an alignment at the middle of the cell is obtained. This creates an equatorial plane.
- During metaphase an additional metaphase checkpoint takes place, which is known as the spindle assembly checkpoint. This checkpoint makes sure the cell is prepared to divide by confirming the order of the chromosomes and the proper attachment of the kinetochores.
- The chromosome alignment is the main difference between mitosis and meiosis, the spindle assembly checkpoint must be occurs during metaphase in both types of cell cycles.
- The cell enters the anaphase when these processes are performed correctly.
Metaphase of Mitosis
- In the cell division cycle, the metaphase is followed up by the condensation of the chromosomes from prophase.
- The condensation is a vital step, it makes sure that the chromosomes (chromatids) do not get damaged due to the pulling and pushing forces that occur in metaphase.
- After the completion of prophase or prometaphase, the chromosomes are randomly organized inside the cell nucleus, within a diffused nuclear membrane.
- Though, the polar and the radial microtubules are still remains connected to each of the chromosomes.
- In mitosis, each chromosome are remains connected to the microtubules from each of the centrosomes, which is consist of two identical sister chromatids. The sister chromatids are connected by cohesins proteins.
- The microtubules permit the cell to be a dynamic element in that they use the forces of pulling and pushing.
- The kinetochore microtubules help to accomplish this by permitting the sister chromatids to get aligned at the center of the cell forming a metaphase plate.
- The tubulin subunits of microtubules are added and removed constantly from the ends of the microtubules. This results in a treadmilling form of movement of the microtubules and the sister chromatids.
- The treadmilling forces also play an important role in the tight holding of the sister chromatids.
- The newly formed cells will be identical, can be confirmed by observing the arrangement of the chromatids along with the metaphase plate.
- The chromatids must be attached to the microtubules from both poles of the cell and aligned at the metaphase plate for the spindle assembly checkpoint to take place.
- The checkpoint increases the duration of metaphase, which can take days to make sure the chromosomes are correctly aligned.
- The chromosomes release a signal after this checkpoint, which activates the anaphase-promoting complex. It leads to the end of metaphase and the beginning of anaphase.
Metaphase of Meiosis
Metaphase I in Meiosis
- In meiosis I the cells involved are analogous, in that a diploid cell divides into haploid (half of the chromosomes).
- It involves the chromosomal crossing over genes creating a genetic difference in the daughter cells of the next generation from the parent cells.
- The meiosis I process initiates with a homologous pair of each chromosome, because before the meiosis process sister chromatids are formed by DNA replication.
- The homologous pair has different alleles, though they are representation of the same DNA.
- During metaphase I, the homologous pairs will attach to each other and they undergo the alignment on the metaphase plate.
- A spindle checkpoint occurs during this phase, known as the meiotic spindle checkpoint. It makes sure that the homologous pairs and each pair are joined to the kinetochore microtubules from each side of the cell before moving to the following phase which is anaphase I.
- Successful metaphase I confirm that the meiosis I phase continues to create two cells each with two copies of half of a full genome.
Metaphase II in Meiosis
- In Metaphase II the 2 daughter cells generated during the first meiotic division, have their meiotic spindles begin to draw the chromosomes to the metaphase plate, again.
- It prepares the centrosome for division in the next phase.
- It occurs after interkinesis (a type of short break).
- This permits the cells to initiate the dividing again, without any DNA replication. Hence, each cell will contain 2 copies of one allele for each gene.
- As the metaphase II begins the nuclear envelope started to breaks down.
- During this stage, 2 kinetochores of each centromere will attach to the spindle fibers from the opposite poles.
- This results in detachment of the sister chromatids of each chromosome in the next phase.
- Additionally, a meiotic spindle checkpoint occurs throughout the separation process of the chromatids for a swift move to the next phase.
Applications of Metaphase
- The genetic abnormalities can be detected during the metaphase stage of cell division by karyotyping. This reason is, during the cross-overs (meiosis) the pulling and pushing of the chromatids by the kinetochore microtubules are take place which may cause damages to the chromosomes if the mitotic spindle checkpoint and the meiotic spindle checkpoint are missed.
Metaphase in Mitosis and Meiosis Video
Difference between Metaphase 1 and Metaphase 2
|Topic||Metaphase 1||Metaphase 2|
|Origin||Metaphase 1 is associated with meiosis 1.||Metaphase 2 is associated with meiosis 2.|
|Arrangement of Chromosomes||Tetrads are arranged at the metaphase equator.||Single chromosomes are arranged at the metaphase equator.|
|Attachment of Chromosomes||Microtubules of one pole are attached to kinetochores of one of the two chromosomes facing to the same pole.||Microtubules are attached to the kinetochores of the centromere on either side of a single chromosome|
|Result||Single chromosomes move towards the opposing poles at anaphase 1.||One pair of sister chromatids move towards the opposing poles at anaphase 2.|
|Metaphase Plate||The metaphase plate is arranged in equidistant to the opposing poles.||The metaphase plate rotates 90 degrees compared to metaphase 1.|
Difference between metaphase of mitosis and metaphase 1 of meiosis
|Topic||Metaphase of mitosis||Metaphase I of meiosis|
|Definition||In mitosis, there is only one division and it produces two daughter cells. Involves one cell division and consequences in two daughter cells.||In meiosis there are two successive divisions, ultimately producing four daughter cells. Involves two successive cell divisions and consequences in four daughter cells|
|Chromosomes division||In the phase, centromeres of the chromosomes undergo division.||Centromeres of chromosome remain undivided.|
|Centromeres arranged||Centromeres are arranged along the equational plane and Chromosomes do not form any loop.||Centromeres remain a little bit any from the equational plane and Chromosomes form loops.|
|Crossing over||The nature of chromosomes remains unchanged as crossing over does not occur.||Crossing over occurs in the substage pachytene and the nature of chromosome remain unchanged|
|Steps||It has only one step. In mitosis, homologous chromosomes pair with each other (i.e., they form tetrads) and crossing-over never occur.||Metaphase of meiosis has two steps such as metaphase-1 and metaphase-2. In meiosis, homologous chromosomes pair with each other (i.e., they form tetrads) and crossing-over occur.|
|Chromosomes Number||Single chromosomes with two chromatids each, line up on the metaphase plate.||Paired chromosomes (bivalents) with four chromatids in each pair line up.|
|Chromosomes align||In metaphase of mitosis, individual chromosomes align there.||In metaphase I of meiosis, tetrads align on the metaphase plate.|
|Daughter cells||Results in diploid daughter cells (chromosome number remains the same as parent cell) and daughter cells are genetically identical.||Results in haploid daughter cells (chromosome number is halved from the parent cell) and daughter cells are genetically different.|
|Occurs||Occurs in all organisms except viruses and creates all body cells (somatic) apart from the germ cells (eggs and sperm)||Occurs only in animals, plants, and fungi and creates germ cells (eggs and sperm) only|
|Duration of Prophase||Prophase is much shorter and no recombination/crossing over occurs in prophase.||Prophase I takes much longer and involves recombination/crossing over of chromosomes in prophase I|
|line up of chromosomes||In metaphase individual chromosomes (pairs of chromatids) line up along the equator.||In metaphase, I pairs of chromosomes line up along the equator.|
|Sister chromatids||During anaphase, the sister chromatids are separated to opposite poles.||During anaphase I the sister chromatids move together to the same pole.|