Which stage of meiotic prophase shows terminalisation of chiasmata as its distinctive feature ?

The correct answer is Diakinesis.

Prophase I of meiosis is a detailed and complex phase divided into five distinct sub-stages: Leptotene, Zygotene, Pachytene, Diplotene, and Diakinesis.

Let us understand the key events occurring in each stage to identify where terminalisation of chiasmata takes place:

1. Leptotene: Chromatin fibers begin to condense, and chromosomes become visible under the light microscope.

2. Zygotene: Homologous chromosomes start pairing up side-by-side, a process called synapsis, facilitated by the formation of the synaptonemal complex.

3. Pachytene: Crossing over occurs between non-sister chromatids of homologous chromosomes, mediated by the recombination nodule.

4. Diplotene: The synaptonemal complex dissolves, and the homologous chromosomes begin to separate from each other except at the sites of crossing over. These X-shaped contact points are called chiasmata.

5. Diakinesis: This is the final stage of meiotic prophase I. It is marked by the terminalisation of chiasmata, where the chiasmata shift or slide towards the tips (ends) of the chromosomes, eventually slipping off as the chromosomes prepare to separate. Other key events in this stage include the breakdown of the nucleolus, disintegration of the nuclear envelope, and assembly of the meiotic spindle.

Therefore, the terminalisation of chiasmata is the distinctive feature of Diakinesis.