Difference Between Anaphase I and Anaphase II

The key difference between anaphase I and anaphase II is that during the anaphase I, homologous chromosomes are separated and are pulled towards the opposite poles while during the anaphase II, sister chromatids are separated and are pulled towards the opposite poles of the cell.

Mitosis and meiosis are two forms of nuclear division that occur in a cell. As a result of mitosis, the nucleus divides into two daughter cells, and each has the same chromosomal number as the parent nuclei. However, in meiosis, the number of nuclear chromosomes that daughter cells have is halved from the parent nuclei. Meiosis occurs during the formation of sex cells such as sperms and eggs in order to carry out sexual reproduction. Hence, as a result of meiosis, one parent cell produces four daughter cells that contain half of the chromosomes of the parent cell.

Furthermore, genetic recombination occurs during the meiosis. Therefore, the resulting gametes are genetically different, and the resulting offspring are also genetically different. Meiosis includes two successive nuclear divisions; i.e. meiosis I and meiosis II. Both meiosis I and meiosis II have four phases, i.e. prophase, metaphase, anaphase, and telophase.

CONTENTS

1. Overview and Key Difference
2. What is Anaphase I
3. What is Anaphase II
4. Similarities Between Anaphase I and Anaphase II
5. Side by Side Comparison – Anaphase I vs Anaphase II in Tabular Form
6. Summary

What is Anaphase I?

Anaphase I is a sub-phase of meiosis I. It begins after metaphase I. During the metaphase I, two homologous chromosome pairs arrange in the equator of the cell, and their centromeres attach with the spindle fibres coming from each pole of the cell. Once this chromosome arrangement is over, the anaphase I starts.

At the beginning of anaphase I, the cell starts to lengthen. As a result of the lengthening of the cell, spindle fibre stretch towards opposite poles, separating the homologous chromosomes into haploid sets. Hence, this is the main event that occurs during the anaphase I. After anaphase I, telophase I begin.

What is Anaphase II?

Anaphase II occurs at meiosis II, which is similar to anaphase of mitosis. Anaphase II follows the metaphase II.  At the end of metaphase II, haploid chromosomes are arranged around the equator of the spindle. Two spindles (one from each pole) attach with the centromere of one chromosome.

When the anaphase I begin, spindle fibres pull haploid chromosomes towards their poles. Due to this force, centromere splits and sister chromatids separate from each other beside the equator. Spindle fibres pull sister chromatids towards their respective poles. Thus, this is the main event that occurs during the anaphase II.

What are the Similarities Between Anaphase I and Anaphase II?

• Anaphase I and anaphase II are two phases of meiosis.
• During these phases, spindle fibres pull chromosomes towards their poles.
• Also, spindle fibres become shorten in both phases.

What is the Difference Between Anaphase I and Anaphase II?

The key difference between anaphase I and anaphase II is that during the anaphase I, complete chromosomes go towards each pole while during the anaphase II, sister chromatids go towards each pole. Anaphase I occurs during meiosis I while the anaphase II occurs during meiosis II. Hence, this is also a difference between anaphase I and anaphase II. Furthermore, anaphase I take place when the cell is in the diploid state while the anaphase II takes place when the cell is in the haploid state. Thus, it is another difference between anaphase I and anaphase II.

Moreover, a further difference between anaphase I and anaphase II is the spindle attachment with the centromeres. In anaphase, I, centromeres of homologous chromosomes are attached to the spindle fibres so as the two spindle fibres are attached to the centromeres of each homologous chromosome. On the other hand, in anaphase II, both spindle fibres are attached to the same chromosome. Besides, during the anaphase, I, centromeres of the chromosomes do not split while during the anaphase II, centromeres split and sister chromatids separate in each chromosome. Hence, it is also a difference between anaphase I and anaphase II.

The below infographic presents more details on the difference between anaphase I and anaphase II.

Summary – Anaphase I vs Anaphase II

Meiosis is one of the two cell divisions. It produces four daughter cells from one parent cell. Each cell contains half of the chromosomes of the parent cell. Meiosis occurs via two main processes; meiosis I and meiosis II. Each meiosis has four subdivisions. Anaphase I occurs in meiosis I while anaphase II occurs in meiosis II. The key difference between anaphase I and anaphase II is that during the anaphase I, the homologues chromosomes are pulled apart and move apart to opposite ends of the cell while during the anaphase II, sister chromatids of each chromosome are separated and are pulled towards the poles. Furthermore, anaphase I occur when the cell is in the diploid state while the anaphase II occurs when the cell is in the haploid state. Thus, this summarizes the difference between anaphase I and anaphase II.

Reference:

1. “Meiosis.” Khan Academy, Khan Academy. Available here 
2. “Meiosis.” Wikipedia, Wikimedia Foundation, 18 Jan. 2019. Available here  

Image Courtesy:

1.”Anaphase-1-meiosis”By Bharghavi Ravi Reddy – Own work, (CC BY-SA 4.0) via Commons Wikimedia  
2.”Anaphase 2″By Bharghavi Ravi Reddy – Own work, (CC BY-SA 4.0) via Commons Wikimedia