Difference Between Anaphase 1 and 2

Main Difference – Anaphase 1 vs 2

Anaphase 1 and anaphase 2 are two phases in the meiotic division of cells which produces gametes during the sexual reproduction. Meiosis is divided into two major phases known as meiosis 1 and meiosis 2. Meiosis 1 is followed by meiosis 2. Anaphase 1 is a sub phase in meiosis 1 and anaphase 2 is a sub phase of meiosis 2. During meiotic division, haploid gametes are produced from diploid germ cells. The main difference between anaphase 1 and 2 is that homologous chromosomes are separated during anaphase 1 whereas sister chromatids are separated during anaphase 2.   

This article looks at, 

1. What is Anaphase 1
      – Process, Function, Features
2. What is Anaphase 2
      – Process, Function, Features
3. What is the difference between Anaphase 1 and 2

What is Anaphase 1

Anaphase 1, which takes place at the meiosis 1, is the phase where homologous chromosomes are separated step. The metaphase 1 is followed by the anaphase 1. During metaphase 1, homologous chromosome pairs are arranged in the metaphase plate and both centromeres are attached to a single kinetochore microtubule. The spindle microtubules are contracted, resulting in a continuous counterbalancing forces on the homologous chromosome pairs. The cohesin protein complexes which bind the two homologous chromosomes together are broken down, separating the two chromosomes from the homologue due to the force generated by the kinetochore microtubules. After the proper bi-orientation of chromosomes, the cell is capable of proceeding into anaphase 1.

During anaphase 1, homologous chromosomes are pulled towards the opposite poles by the shortening of kinetochore microtubules. The non-kinetochore microtubules are lengthened in order to push the chromosomes further apart. Homologous chromosomes are separated from the cohesin at the arms of the chromosomes. Each separated bivalent chromosome starts moving towards the opposite poles due to the tension generated by the microtubules. Anaphase 1 is followed by telophase 1 where the bivalent chromosomes arrive at the opposite poles. The first division of the cytoplasm is initiated at the anaphase 1. 

Figure 1: Phases of Mitosis

What is Anaphase 2

Anaphase 2, which takes place at the meiosis 2, is the step where sister chromatids are separated. Metaphase 2 is followed by anaphase 2. During metaphase 2, two kinetochore microtubules, each from two opposite poles, are attached to the same centromere of the individual chromosomes. These bivalent individual chromosomes are aligned at a new equatorial metaphase plate which is rotated by 90º relative to the anaphase 1. The proper arrangement of the individual chromosomes at the equatorial plate, binding with the kinetochore microtubules lets the cell to proceeds into the anaphase 2. During anaphase 2, the centromeric cohesion protein complexes are cleaved due to the contacting tension of the kinetochore microtubules on the centromere of the each individual chromosome. Thus, the bivalent chromosomes are separated into two sister chromatids. Each sister chromatid is now known as a daughter chromosome. Further contraction of the kinetochore microtubules pulls each daughter chromosome towards the opposite poles. Anaphase 2 is followed by the telophase 2 where the formation of the haploid nuclei at the opposite poles is taken place. 

Figure 2: Anaphase 2

Difference Between Anaphase 1 and 2

Meiosis Phase

Anaphase 1: Anaphase 1 takes place during meiosis 1.

Anaphase 2: Anaphase 2 takes place during meiosis 2.

Haploid vs Diploid

Anaphase 1: Anaphase 1 occurs in diploid cells.

Anaphase 2: Anaphase 2 occurs in haploid cells.

Spindle Fibers

Anaphase 1: Two spindle fibers are attached to the centromere of the each chromosome in the homologous pair.

Anaphase 2: Two spindle fibers are attached to the same centromere of a single chromosome.

Separation During the Phases

Anaphase 1: Homologous chromosomes are separated during anaphase 1.

Anaphase 2: Sister chromatids are separated during anaphase 2.

Splitting of the Centromere

Anaphase 1: The centromeres of each chromosome in the homologous pair remain untouched.

Anaphase 2: Two sister chromatids are separated by splitting the centromere.

Anaphase

Anaphase 1: Anaphase 1 is not similar to the anaphase of the mitosis.

Anaphase 2: Anaphase 2 is similar to the anaphase of the mitosis.

Plane

Anaphase 1: During anaphase 1, homologous chromosomes are arranged in the cell equator.

Anaphase 2: During anaphase 2, individual chromosomes are arranged in a plane which is rotated by 90º relative to the anaphase 1.

Separation of the Cohesin Protein Complex

Anaphase 1: The cohesin proteins at the chromosomal arms are cleaved during the anaphase 1.

Anaphase 2: The cohesin protein complexes at the centromere are cleaved during the anaphase 2.

End Result

Anaphase 1: Chromosomes are present at the opposing poles at the end of the anaphase 1.

Anaphase 2: Sister chromatids are present at the opposing poles at the end of the anaphase 2.

Conclusion

Anaphase 1 and 2 are two phases that take place in meiosis 1 and meiosis 2 stages respectively.  Anaphase 1 takes place in 4n cells whereas anaphase 2 takes place in 2n cells. Anaphase 1 produces a 2n cell from the 4n cell. Anaphase 2 produces an n cell from a 2n cell. During anaphase 1, a single kinetochore-microtubule is attached to each of the chromosomes in the homologous chromosome pair. During anaphase 2, two kinetochore microtubules, each from one pole of the two opposite poles, attach to the same centromere of the bivalent chromosome. Contraction of the kinetochore microtubules lets the separation of either homologous chromosome pair or the individual chromosome into chromosomes and sister chromatids respectively. Therefore, the main difference between anaphase 1 and 2 is their separations at the equatorial plate.

Reference:
1.”Meiosis”. En.wikipedia.org. N.p., 2017. Web. 9 Mar. 2017.
2.”Pearson – The Biology Place”. Phschool.com. N.p., 2017. Web. 9 Mar. 2017.
3.”Pearson – The Biology Place”. Phschool.com. N.p., 2017. Web. 9 Mar. 2017.

Image Courtesy:
1. “Meiosis Stages”By Ali Zifan – Own work; Used information from Campbell Biology (10th Edition) by: Jane B. Reece & Steven A. Wasserman (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