Q.What are the various stages of Meiotic Prophage-1? Write the chromosomal events during each stage.

Prophase I of meiosis is divided into five sub-stages (Leptotene -> Zygotene -> Pachytene -> Diplotene -> Diakinesis), during which homologous chromosomes pair, recombine, and prepare to separate.

1. Leptotene:

Chromosomes begin to condense and become visible under the microscope as long, thin, single threads. Compaction of chromatin starts.

2. Zygotene:

Homologous chromosomes start to pair up — this pairing is called synapsis. A protein structure, the synaptonemal complex, forms between the paired homologues. Each pair of synapsed homologous chromosomes is called a bivalent or tetrad (as it consists of 4 chromatids).

3. Pachytene:

Chromosomes continue to condense further. Crossing over occurs — non-sister chromatids of the homologous chromosomes exchange genetic material at points called chiasmata, mediated by the enzyme complex recombinase, aided by recombination nodules. This stage is responsible for genetic recombination/variation.

4. Diplotene:

The synaptonemal complex dissolves, and the homologous chromosomes of each bivalent start to separate from each other, but they remain connected at the points of crossing over (chiasmata). This gives a characteristic cross-shaped appearance. …