metaphase/anaphase transition of meiosis I

Definition

Target type: biologicalprocess

The cell cycle process in which a cell progresses from metaphase to anaphase as part of meiosis I. [ISBN:0815316194]

The metaphase-anaphase transition in meiosis I is a crucial stage characterized by the separation of homologous chromosomes, ensuring that each daughter cell receives one copy of each chromosome. This process is tightly regulated and involves a series of key events:

1. **Chromosomal Alignment**: Homologous chromosome pairs, connected by chiasmata (crossover points), align at the metaphase plate. This alignment ensures that each daughter cell will receive one chromosome from each pair.

2. **Spindle Fiber Attachment**: Microtubules from opposite poles of the spindle apparatus attach to the kinetochore, a protein complex at the centromere of each chromosome.

3. **Separation of Homologues**: Once all chromosomes are correctly aligned, a crucial signal triggers the breakdown of cohesin, a protein complex that holds sister chromatids together. This allows the homologues to separate and move toward opposite poles of the cell.

4. **Sister Chromatids Remain Connected**: Importantly, sister chromatids remain attached at their centromeres, ensuring that they are pulled to the same pole of the cell. This is a key difference from mitosis, where sister chromatids separate at anaphase.

5. **Cytokinesis Begins**: As the homologues move apart, the cell begins the process of cytokinesis, which divides the cytoplasm and forms two daughter cells.

6. **The Transition Triggers**: The transition from metaphase to anaphase is triggered by the activation of the anaphase-promoting complex/cyclosome (APC/C), a ubiquitin ligase. APC/C targets specific proteins for degradation, including securin, which holds the separase enzyme in an inactive state. Upon securin degradation, separase becomes active and cleaves cohesin, allowing the homologues to separate.

The metaphase-anaphase transition in meiosis I is essential for ensuring the correct segregation of chromosomes and the production of haploid gametes. Errors in this process can lead to aneuploidy (abnormal chromosome number), which can result in developmental abnormalities or infertility.'
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