Separation of Paired Homologous Chromosomes

The separation of paired homologous chromosomes occurs during a specific stage of meiosis called diakinesis.

Explanation:

During meiosis, the process of cell division that produces gametes (sperm and eggs), there are two rounds of cell division - meiosis I and meiosis II. Meiosis I is the stage where homologous chromosomes pair up and exchange genetic material in a process called crossing over.

The different stages of meiosis I are:

1. Prophase I: This is the longest phase of meiosis and can be further divided into five substages - leptotene, zygotene, pachytene, diplotene, and diakinesis.

2. Zygotene: During this stage, homologous chromosomes begin to pair up and align along their entire length. This pairing is called synapsis, and a structure called the synaptonemal complex holds the chromosomes together.

3. Pachytene: In this stage, the homologous chromosomes continue to condense and become even more tightly paired. Crossing over occurs during pachytene, where sections of genetic material are exchanged between non-sister chromatids of homologous chromosomes.

4. Diplotene: In diplotene, the paired homologous chromosomes start to separate from each other. However, they remain connected at specific points called chiasmata, where crossing over has occurred. The synaptonemal complex begins to break down, and the chromosomes start to uncoil.

5. Diakinesis: This is the final stage of prophase I, where the homologous chromosomes fully separate from each other. They become highly condensed, and the nuclear envelope begins to break down. The chiasmata are still visible, and the spindle fibers start to attach to the chromosomes.

Conclusion:

The stage during which the separation of paired homologous chromosomes begins is diakinesis. It is the final stage of prophase I and marks the completion of the pairing and crossing over of homologous chromosomes.

(b) Diplotene stage.