The appearance of recombination nodules on homologous chromosomes during meiosis characterizes:
Answer: (C) Sites at which crossing over occurs. Answer: (C) Sites at which crossing over occurs Solution: Recombination nodules are protein assemblies that appear on the paired homologous chromosomes (the bivalent within the synaptonemal complex) at the precise points where crossing over (exchange of segments) takes place during pachytene of meiosis I.
- A.Synaptonemal complex
- B.Bivalent
- C.Sites at which crossing over occurs✓
- D.Terminalization
Correct Answer
(C) Sites at which crossing over occurs
Solution & Explanation
Answer: (C) Sites at which crossing over occurs Solution: Recombination nodules are protein assemblies that appear on the paired homologous chromosomes (the bivalent within the synaptonemal complex) at the precise points where crossing over (exchange of segments) takes place during pachytene of meiosis I. Crossing over is the physical basis of recombination, generating non-parental gene combinations. Hence their appearance marks the sites at which crossing over occurs, not the complex or the bivalent themselves. NCERT Reference: NCERT Class XII, Ch 4, p.67, lines 38-40: "the term recombination to describe the generation of non-parental gene combinations" (recombination nodules mark crossing-over sites; the nodule term itself is an extension of this NCERT description of recombination).