Question

During which phase of meiosis, synaptonemal complex begins to form?

• A. Anaphase
• B. Metaphase
• C. Pachytene
• D. Zygonema

Hint:

Remember the stages of Prophase I: \[ \text{Leptotene} \rightarrow \text{Zygotene} \rightarrow \text{Pachytene} \rightarrow \text{Diplotene} \rightarrow \text{Diakinesis} \]
• Zygotene \(\rightarrow\) Synapsis begins
• Pachytene \(\rightarrow\) Crossing over occurs

Answer 1

The Correct Option is D

Concept: During prophase I of meiosis, homologous chromosomes pair with each other in a process called synapsis. Prophase I is divided into five stages:
• Leptotene
• Zygotene (Zygonema)
• Pachytene
• Diplotene
• Diakinesis The synaptonemal complex is a protein structure that forms between homologous chromosomes and facilitates pairing and recombination.

Step 1: Understanding when synaptonemal complex forms. During: \[ \text{Zygotene (Zygonema)} \] homologous chromosomes begin pairing through synapsis. At this stage: \[ \text{Synaptonemal complex begins to form} \] Therefore: \[ \boxed{\text{Synaptonemal complex begins to form during Zygonema}} \]

Step 2: Understanding the role of Pachytene. In Pachytene:
• Synapsis becomes complete
• Crossing over occurs Thus, the complex is already fully formed by Pachytene.

Step 3: Eliminating the incorrect options.
• Option (A): Anaphase involves chromosome separation.
• Option (B): Metaphase involves chromosome alignment at the equatorial plate.
• Option (C): Pachytene is the stage where crossing over occurs after synaptonemal complex formation. Hence, the correct answer is Zygonema. \[ \boxed{\text{Zygonema} \Rightarrow \text{Beginning of synaptonemal complex formation}} \]