Question

In which stage do chromosomes appear as thin long threads?

• A. Zygotene
• B. Pachytene
• C. Leptotene
• D. Prophose

Answer 1

Answer: (C)

Leptotene

The Prophase-I of the Meiosis-I has following sub-phases:

a) Leptotene- It is the beginning of the prophase and the chromosomes appear as thin long threads. The condensation of chromosome is still not done by this phase.

b) Zygotene- By this phase, the homologous chromosomes start pairing up and the chromosomes appear condensed and thick. The synaptonemal complex is also visible.

c) Pachytene- This phase marks the exchange of parts between the non-sister chromatids of the homologous chromosomes called the crossing-over. The point of attachment of the non-sister chromatids, called the chiasma (pl. chiasmata) is also visible.

d) Diplotene- The crossing over is completed and the synaptonemal complex is dissolved. The homologous chromosomes start pulling away from each other.

e) Diakinesis- By this stage, the nuclear membrane and the nucleolus disppear and the homologous chromosomes move away from the point of the chiasma.

Hence, the correct answer is 'Leptotene'