Crossing over takes place between which chromatids and in which stage of the cell cycle ?
Answer: (B) Non-sister chromatids of homologous chromosomes at Pachytene stage of prophase I.. Answer: Non-sister chromatids of homologous chromosomes at Pachytene stage of prophase I.
- A.Non-sister chromatids of non-homologous chromosomes at Zygotene stage of prophase I.
- B.Non-sister chromatids of homologous chromosomes at Pachytene stage of prophase I.✓
- C.Non-sister chromatids of homologous chromosomes at Zygotene stage of prophase I.
- D.Non-sister chromatids of non-homologous chromosomes at Pachytene stage of prophase I.
Correct Answer
(B) Non-sister chromatids of homologous chromosomes at Pachytene stage of prophase I.
Solution & Explanation
Answer: Non-sister chromatids of homologous chromosomes at Pachytene stage of prophase I. Solution: Crossing over is the exchange of genetic material between non-sister chromatids of homologous (not non-homologous) chromosomes, and it occurs at the pachytene stage of prophase I, marked by recombination nodules. Zygotene is only synapsis (pairing), and the chromatids must be non-sister and from homologous chromosomes for recombination. NCERT Reference: Ch 10, p.126, lines 59-60 — "crossing over occurs between non-sister chromatids of the homologous chromosomes"