Question: 95: The appearance of recombination nodules on homologous chromosomes during meiosis characterizes :
(1) Sites at which crossing over occurs
(2) Terminalization
(3) Synaptonemal complex
(4) Bivalent
Answer: Option (1)
Explanation:
During prophase I of meiosis, homologous chromosomes pair with each other and undergo synapsis.
Recombination nodules appear on the synaptonemal complex during the pachytene stage of prophase I.
These recombination nodules represent the exact sites where genetic exchange between non-sister chromatids takes place.
The exchange of genetic material at these sites is known as crossing over, which results in genetic recombination.
Terminalization refers to the movement of chiasmata towards the ends of chromosomes during diplotene, not the appearance of recombination nodules.
The synaptonemal complex is the protein structure that holds homologous chromosomes together but is not itself defined by recombination nodules.
A bivalent refers to a pair of homologous chromosomes, not specifically to the sites of recombination.
Therefore, recombination nodules characterize the sites at which crossing over occurs,
making option (1) correct.