Difference between Anaphase I and Anaphase II

The difference between anaphase I and anaphase II is that in anaphase I, homologous chromosomes are being separated from each other while in anaphase II, sister chromatids are separated from each other.

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Cell division is of two types in eukaryotes, mitosis, and meiosis. In mitosis, one cell is divided into two daughter cells and the number of chromosomes is the same in each daughter cell. In meiosis, one cell is divided into four progeny cells and the number of chromosomes remains half in each daughter cell.  Meiosis is divided into two phases, meiosis I and meiosis II. Both phases, i.e. meiosis I and meiosis II have differences in their steps. Anaphase I is the part of meiosis I and anaphase II is the part of meiosis II. In meiosis I, homologous chromosomes are separated during anaphase while during the stage of anaphase II in meiosis II, sister chromatids of a chromosome are separated.

Anaphase I is carried out by diploid cells while anaphase II is carried out by haploid cells.

During the process of anaphase I, the centromere is not further split, rather it remains intact because homologous chromosomes are being segregated while in anaphase II, two centromeres are divided and separated now sister chromatids are being segregated.

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During anaphase, I, a pair of homologous chromosomes that makes a bivalent, its members repel each other and go towards the poles of opposite sides. Each pole of the nucleus now has half the number of chromosomes. The movement of homologous chromosomes is carried out by spindle fibers.  During anaphase II, sister chromatids of each chromosome are segregated after the division of centromere. Now, these chromatids move towards the poles of opposite sides. This step of meiosis resembles mitosis. Now each pole of the nucleus contains a single chromatid with an equal number of chromosomes.

In anaphase, I, the separated genetic material (homologous chromosomes) is not further modified while in anaphase II, the separated genetic material, i.e. chromatids are further modified and converted to chromosomes.

During anaphase I, spindle fibers are joined with the centromeres of two different sets of chromosomes which are attached with each other while in anaphase II,  two spindle fibers are joined with one centromere of single chromosomes which contain two sister chromatids.

Anaphase I does not have any resemblance with the anaphase of meiosis II or mitosis while on the other hand, anaphase II has similarity with the anaphase of mitosis.

At the end of anaphase I, homologous chromosomes are found at the opposite poles of the nucleus while at the end of anaphase II, sister chromatids are found at the opposite poles of the nucleus.

Comparison Chart

Basis Anaphase IAnaphase II
Occurs in It is the step of meiosis IIt is the step of meiosis II.
Key difference During this step, homologous chromosomes are segregated.During this step, the sister chromatids of each chromosome are segregated.
Takes place in which type of cells It takes place in diploid cells.It takes place in a haploid cell.
Aim The aim is to reduce the number of chromosomes up to half in the progeny cells.The aim is to generate four daughter cells with a haploid number of chromosomes.
What is segregated? During this step, two different sets of chromosomes are being separated and go to the opposite poles of the nucleus.During this step, the sister chromatids of the same chromosome are being separated and go towards the opposite poles of the nucleus.
Role of centromere During this process, the centromere is not split. It remains intact because the whole chromosome moves towards the opposite side.During this process, the centromeres of both homologous chromosomes are split because now, the chromatids of the same chromosome move in the opposite direction.
Spindle fibers are attached with In this step, spindle fibers join the centromeres of two different sets of chromosomes separately.In this step, spindle fiber joins the single centromere of one chromosome because now the sister chromatids are required to be separated.
Similarity This step does not have any resemblance with anaphase II or anaphase of mitosis.This step has a similarity with the anaphase of mitosis.
At the end of phase At the end of this phase. Homologous chromosomes are found at the opposite poles of the nucleus.At the end of this phase, sister chromatids are found at the opposite poles of the nucleus.
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What is Anaphase I?

Anaphase I is the third step of meiosis I. Meiosis I is the first step of meiosis, a type of cell division in which a single cell divides to form four daughter cells and the number of chromosomes remains half in each progeny cell. During anaphase I of meiosis, homologous chromosomes are segregated from each other and go to the opposite poles of the nucleus. At the start of this phase, the length of the cell and the nucleus starts to increase, the chromosomes are settled at the equator of the nucleus and spindle fibers join the centromeres of each set of chromosomes. These spindle fibers exert force and pull the chromosomes towards the opposite sides of the nucleus resulting in the settlement of chromosomes at the opposite poles. Anaphase I takes place in diploid cells and its aim is to produce the cells having half the number of chromosomes. The sister chromatids of each chromosome remain attached during anaphase I. Division of the centromere also does not happen during anaphase I. At the end of anaphase I, each pole attains one homologous chromosome which will then go to each daughter cell.

What is Anaphase II?

Anaphase II is the third step in the meiosis II in which the sister chromatids are being segregated. This phase takes place in haploid cells which are formed as a result of meiosis I. During this phase, each homologous chromosome is joined by spindle fibers by the opposite poles which exert force and pull the sister chromatids towards opposite sides. Finally, centromeres of each chromosome are split, chromatids are being separated and go to the opposite pole. Later, these chromatids are arranged to form chromosomes. In this step, the arrangement of chromatids is rotated to the angle of ninety degrees from that of anaphase I. This step resembles with the anaphase of mitosis because the number of chromosomes remains the same after the division.

Key differences between Anaphase I and Anaphase II

  1. Anaphase I is the step of meiosis I while anaphase II is the step of meiosis II.
  2. During anaphase, I, the segregation of homologous chromosomes takes place while during anaphase II, segregation of sister chromatids is carried out.
  3. During anaphase I, the centromere is not split while during anaphase II, centromere splits.
  4. Anaphase I does not resembles anaphase II or anaphase of mitosis while anaphase II has similarity with the anaphase of mitosis.
  5. Anaphase I takes place in diploid cells while anaphase II takes place in haploid cells.

Conclusion

Both anaphase I and anaphase II are the phases of meiosis which is the part and parcel of sexual reproduction in human beings and other animals. It is very important for biology students to know the differences between anaphase I and anaphase II. In the above article, we came across the clear differences between anaphase I and anaphase II.

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