Difference Between Metaphase 1 and 2

Main Difference – Metaphase 1 vs Metaphase 2

Metaphase is one of the four stages of nuclear division in eukaryotic cells. The four stages of cell division in eukaryotes include prophase, metaphase, anaphase and telophase. During metaphase, chromosomes of a cell are condensed to their second-most condensed stage. Membrane nucleus breaks down, and the condensed chromosomes align in the cell equator in metaphase. Cell equator is referred to as metaphase plate or the equatorial plate. In meiosis, two nuclear divisions, meiosis 1 and meiosis 2 occur to produce diploid germ cells. Metaphase 1 is associated with meiosis 1 whereas the metaphase 2 is associated with meiosis 2. The main difference between metaphase 1 and 2 is that chromosomes are attached as homologous pairs at the equator during the metaphase 1 and during metaphase 2, single chromosomes are attached at the equator.

 This article explains,

1. What is Metaphase 1
2. What is Metaphase 2
3. What is the difference between Metaphase 1 and  2

What is Metaphase 1

During metaphase 1, homologous pairs of chromosomes (tetrads) are attached to the meiotic spindle at the metaphase plate. Prior to metaphase 1, kinetochores form around the centromere. Kinetochore is a protein variety which attach the centromere to the microtubules of the spindle. The opposite poles bear centrioles of the cell. Highly coiled and densed chromosome pairs are attached to the microtubules of the meiotic spindle via kinetochores. The chromosome pairs are arranged in equidistant from the poles due to the counterbalance of pulling powers created by microtubules towards the opposing poles. Microtubules from one pole are attached to kinetochores of one chromosome, facing towards that pole. On the other hand, the microtubules of the other pole are attached to the kinetochores of the second chromosome facing towards the second pole.

Figure 1: Metaphase 1

What is Metaphase 2

Metaphase 2 is very similar to metaphase in mitosis. During metaphase 2, individual chromosomes are arranged at the metaphase plate. Single chromosomes are attached to the microtubules of the meiotic spindle via kinetochores of each centromere. Sister chromatids of each chromosome are separated apart due to the pulling power created by microtubules. In metaphase 2, metaphase plate rotates in 90 degrees from the metaphase plate generated at metaphase I.

Figure 2: Metaphase 2

Difference Between Metaphase 1 and  2

Origin

Metaphase 1: Metaphase 1 is associated with meiosis 1.

Metaphase 2: Metaphase 2 is associated with meiosis 2.

Arrangement of Chromosomes

Metaphase 1: Tetrads are arranged at the metaphase equator.

Metaphase 2: Single chromosomes are arranged at the metaphase equator.

Attachment of Chromosomes

Metaphase 1: Microtubules of one pole are attached to kinetochores of one of the two chromosomes facing to the same pole.

Metaphase 2: Microtubules are attached to the kinetochores of the centromere on either side of a single chromosome.

Result

Metaphase 1: Single chromosomes move towards the opposing poles at anaphase 1.

Metaphase 2: One pair of sister chromatids move towards the opposing poles at anaphase 2.

Metaphase Plate

Metaphase 1: The metaphase plate is arranged in equidistant to the opposing poles.

Metaphase 2: The metaphase plate rotates 90 degrees compared to metaphase 1.

Conclusion

In classical cytogenetics, it is very important to analyze the metaphase chromosomes. Most condensed and coiled chromosomes generated in metaphase makes the analysis easy at this stage. Cells in short-term cultures can be arrested at metaphase by using inhibitors.

Reference:

1. “Metaphase”. Learn Science at Scitable
2. “Concept 5: Meiosis I: Metaphase I”. Pearson-The Biology page.
3. “Metaphase 2”. Stages of Meiosis.

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