Anaphase in Mitosis and Meiosis (Anaphase I, II)

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Last Updated on August 27, 2020 by Sagar Aryal

Anaphase Definition

This is the phase that separates duplicate genetic materials that are carried in the nucleus of the parent cell, into the two identical daughter cells.

  • In the previous phase, metaphase, the sister chromatids (replicated chromosomes) are aligned along the cell’s equator on the metaphase plate.
  • Therefore, during anaphase, each pair of chromosomes separates into two identical but independent chromosomes.
  • Each of these chromosomes gets separated by mitotic spindles known as microtubules, attached to the chromosomes at both ends of the cell.
  • Separation occurs simultaneously at the centromere and each separated chromosome gets pulled by the spindles to the opposite poles of the cell.
  • The function of anaphase is to ensure that each daughter cell receives identical sets of chromosomes before the final phase of the cell cycle, which is telophase.

Anaphase in Mitosis and Meiosis

Image Source: Wikipedia and Wikipedia (Ali Zifan).

What happens during anaphase?

  • Anaphase begins when the anaphase-promoting complex which terminates the metaphase.
  • This anaphase-promoting complex tags securin, a protein that helps in the transition from metaphase to anaphase and also used for the destruction of securin by incorporating ubiquitin hence acting as an inhibitory chaperone.
  • Securin acts by inhibiting the separase enzyme, a type of protease. When securin is destroyed, the separase enzyme is released which then breaks down cohesin protein which holds the sister chromatids together.
  • Several unique microtubules are involved in the creation of the forces required for the separation of chromatids. These include Astral microtubules, kinetochore microtubules, and the interpolar microtubules.
  • This leads to the splitting of the centromere, pulling the sister chromatids to the poles of the cell by the kinetochore microtubules.
  • The separated sister chromatids then form a V or Y-shape at either pole of the cell.
  • The astral and interpolar microtubules contribute to the stretching and shaping of the cell which takes up an oval shape.
  • Separation of the chromatids into single sister chromosomes means that they contain the same genetic information but function independently as new cells.
  • Successful completion of anaphase leads to the next phase of the cell cycle which is telophase.

Anaphase in mitosis

Anaphase

Figure: Anaphase in Mitosis. Image Source: Wikipedia

  • Anaphase in mitosis is triggered by the separation of the sister chromatids with the help of separase.
  • Separase breaks the cohesion that binds the sister chromatids, as the microtubules pull the sister chromatids towards the opposite plea of the cells.
  • The astral and interpolar microtubules play a major role in lengthening and elongating the cell which takes an oval shape.

Anaphase in meiosis

  • The anaphase of meiosis is made up of two consecutive cell divisions, i.e anaphase I and anaphase II.
  • In this stage of meiosis, since there is no DNA replication in between, the diploid cell with two alleles for each gene gets reduced to a haploid cell containing a single allele at each gene.
  • Generally, anaphase I involve separating the chromosomes from each sister chromatid to the opposite poles still attached to the microtubules of the cell while anaphase 2 involves the actual split of the sister chromatids into single chromatids.

Anaphase I

Anaphase I in Meiosis

Figure: Anaphase I in Meiosis. Image Source: Wikipedia (Ali Zifan).

  • During this phase, the kinetochore microtubules shorten thus pulling the homologous chromosomes to opposite poles of the cell.
  • The non-kinetochore microtubules start to lengthen thus pushing the centrosomes apart.
  • The cell also elongates as it prepares for dividing at the center.
  • The cohesins around the centromere remain protected by a protein known as Shugoshin (guardian spirit), preventing the sister chromatids from separating while the homologs are segregated.

Anaphase II

Anaphase II in Meiosis

Figure: Anaphase II in Meiosis. Image Source: Wikipedia (Ali Zifan).

  • This is the phase after metaphase 2 whereby the remaining centromeric cohesins which are not protected by the Shugoshin anymore are cleaved.
  • This allows the separation of the sister chromatids which are then singly referred to as sister chromosomes. They move towards the opposite poles of the cells.

Video Animation: What happens in anaphase? (Video By: MooMooMath and Science)

Reference and Sources

  • https://www.expii.com/t/anaphase-definition-diagrams-10161
  • Lumenlearning.com/Biology For Major
  • https://teaching.ncl.ac.uk/bms/wiki/index.php/Anaphase
  • https://www.nature.com/scitable/definition/anaphase-179/
  • https://en.wikipedia.org/wiki/Meiosis#Anaphase_I
  • https://en.wikipedia.org/wiki/Anaphase
  • https://www.khanacademy.org/science/biology/cellular-molecular-biology/mitosis/a/phases-of-mitosis
  • http://www.phschool.com/science/biology_place/biocoach/mitosisisg/anaphase.html

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