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: (B) 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: (B) 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 (paired) chromosomes, and it occurs during the pachytene stage of prophase I of meiosis. NCERT Ch 4 establishes that the two alleles lie on homologous sites of homologous chromosomes and that recombination generates non-parental combinations; the precise pachytene timing is detailed in the Class XI Cell Cycle and Cell Division chapter. NCERT Reference: NCERT Class XII, Ch 4, p.65, lines 027-029: "chromosomes as well as genes occur in pairs. The two alleles of a gene pair are located on homologous sites on homologous chromosomes."