Anaphase of mitosis and meiosis

General stage characteristics

Anaphase (Anaphase) is one of the most dynamic and critically important stages of nuclear and cellular division. The main motor mechanism driving this stage is the shortening of the spindle fibers. It is precisely this mechanical pull that moves the genetic material in a strictly organized manner toward opposite poles of the dividing cell.

It is important to understand that the specific scenario of what exactly separates and moves to the poles differs fundamentally between the mitotic cycle and the various stages of meiosis. The behavior of the centromeres plays a key role here: whether they divide or remain intact determines whether individual sister chromatids separate or whole chromosomes move to the poles.

Anaphase of mitosis

Mitosis ensures the precise distribution of genetic information, in which daughter cells receive copies of the maternal set. During the anaphase stage of mitosis, a crucial event occurs: centromeres divide.

• The shortening spindle fibers pull sister chromatids apart to opposite poles.
• From the moment of physical separation, these chromatids acquire the status of independent chromosomes.
• Dynamics of genetic material: since each original two-chromatid chromosome has divided in two, the total number of chromosomes in the cell temporarily doubles. The total genetic formula of the cell at this stage is 4n4c.

By comparison, in the preceding prophase and metaphase the set was equal to 2n4c, and in the subsequent telophase each daughter cell will receive the standard diploid set 2n2c.

Anaphase I (First meiotic division)

The first division of meiosis is reductional, and its anaphase has a fundamental difference from the analogous stage of mitosis.

• Centromeres do not divide. This is a fundamental fact that defines the essence of reductional division.
• Whole homologous chromosomes move to the poles of the cell. It is important to emphasize that each of these chromosomes is still two-chromatid (consists of two chromatids).
• Genetic formula: in total, the cell maintains a set of 2n4c until cytokinesis is complete.

Thus, in anaphase I there is no temporary increase in the chromosome number, as sister chromatids remain tightly linked at the centromere region, and only homologous partners separate.

Anaphase II (Second meiotic division)

Meiosis II, also called equational division, is very similar in its mechanics to standard mitosis, but it occurs in cells with a different initial genetic status. This stage is preceded by prophase II (chromatin condensation) and metaphase II (alignment of chromosomes at the equator).

• In anaphase II, just as in mitosis, centromeres divide.
• Daughter chromosomes (which were previously called sister chromatids) move to the poles.
• Genetic formula: in total, the set in each dividing cell is 2n2c. Here, a temporary doubling of the chromosome number occurs, but relative to the haploid set inherited by the cell after the first division. As a result, following telophase II, four fully formed haploid cells will be generated.

Class and exam questions

What else to study on this topic

• Dynamics of genetic material in prophase, metaphase, and telophase of mitosis.
• Processes of prophase II (chromatin condensation) and metaphase II.
• Telophase II and the mechanism of formation of four haploid cells.
• The role of kinetochores, chiasmata, and telomeres in cell division.
• Synapsis and crossing over as processes preceding chromosome segregation.

Other topics in the "Gametogenesis" section

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