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Biology Question 111 – NEET-UG 2023

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

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Ninja Strategy•Event-Stage Mapping

Recall the specific key event associated with each sub-stage of Prophase I; recombination nodules are directly linked to crossing over, which occurs in Pachytene.

Step 1: Understand Prophase I Sub-stages✦ Active

Prophase I of meiosis is a prolonged stage divided into five sub-stages: Leptotene, Zygotene, Pachytene, Diplotene, and Diakinesis. Each stage is characterized by specific chromosomal events.

Step 2: Identify the Stage of Recombination○ Expand

Genetic recombination, or crossing over, is a crucial event in meiosis that leads to genetic variation. This process occurs during the pachytene sub-stage. During pachytene, homologous chromosomes are fully paired (synapsed), and the exchange of genetic material takes place between non-sister chromatids.

💡 Teacher's Secret Hint

Remember that synapsis (pairing of homologous chromosomes) occurs in Zygotene, but crossing over itself happens in Pachytene.

Step 3: Relate Recombination to Nodules○ Expand

Recombination nodules are enzyme-mediated structures that appear at the sites where crossing over occurs. Since crossing over takes place during the pachytene stage, the appearance of recombination nodules is also characteristic of the pachytene sub-stage of prophase I.

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