In meiosis crossing over is initiated at:
Answer: (A) Pachytene. Answer: Pachytene Solution: Crossing over is initiated during pachytene, the stage marked by the appearance of recombination nodules where exchange of genetic material occurs between non-sister chromatids of homologous chromosomes.
- A.Pachytene✓
- B.Leptotene
- C.Zygotene
- D.Diplotene
Correct Answer
(A) Pachytene
Solution & Explanation
Answer: Pachytene Solution: Crossing over is initiated during pachytene, the stage marked by the appearance of recombination nodules where exchange of genetic material occurs between non-sister chromatids of homologous chromosomes. Leptotene only shows gradual chromosome compaction and zygotene involves synapsis (pairing), both before any exchange begins. By diplotene crossing over is already complete and the homologues begin to separate, leaving chiasmata, so it is too late for initiation. NCERT Reference: Ch 10, p.126, lines 58-59 — "the sites at which crossing over occurs between non-sister chromatids"