Question

The process of appearance of recombination nodules occurs at which sub stage of prophase I in meiosis?

• A. Pachytene
• B. Diplotene
• C. Diakinesis
• D. Zygoten

Answer 1

The Correct Option is A

The process of appearance of recombination nodules during meiosis corresponds to a specific sub-stage of prophase I. Let's break down the stages of prophase I to determine where this process takes place:

1. Leptotene: This is the initial phase where chromosomes begin to condense and become visible. At this point, they appear as long and thin strands.
2. Zygotene: During this stage, homologous chromosomes start pairing along their length, known as synapsis. However, recombination nodules are not typically characterized in this stage.
3. Pachytene: This is the stage where recombination nodules are commonly witnessed. Here, the synaptonemal complex has completely formed, and homologous chromosomes tightly pair with each other. Genetic recombination (crossing over) occurs in this stage at recombination nodules, leading to genetic variability.
4. Diplotene: At this point, the synaptonemal complex begins to disassemble, and homologs start to separate slightly while remaining attached at points called chiasmata, where crossing over has occurred.
5. Diakinesis: Chromosomes further condense, and the chiasmata move toward the ends of chromosomes, terminalizing as the cell prepares for metaphase I.

Thus, the correct answer is Pachytene, during which recombination nodules appear, and crossing over takes place.

Other options can be ruled out as follows:

• Diplotene: This is the stage after pachytene where synapsis ends, and homologs start to separate, indicating that recombination nodules have already served their purpose.
• Diakinesis: This is the final stage of prophase I, focused primarily on preparation for segregation rather than recombination.
• Zygotene: While synapsis begins here, recombination nodules do not appear at this stage.