Question

Arrange the following sequence in descending order :
• [A.] Zygotene
• [B.] Diakinesis
• [C.] Pachytene
• [D.] Diplotene
Choose the correct answer from the options given below :

• A. B-A-D-C
• B. B-A-C-D
• C. B-D-A-C
• D. B-D-C-A

Hint:

Remember the Prophase-I sequence: Leptotene \(\rightarrow\) Zygotene \(\rightarrow\) Pachytene \(\rightarrow\) Diplotene \(\rightarrow\) Diakinesis.

Answer 1

The Correct Option is D

Concept: These stages belong to: \[ Prophase-I of meiosis \] The stages of Prophase-I occur in the following order: \[ \text{Leptotene} \rightarrow \text{Zygotene} \rightarrow \text{Pachytene} \rightarrow \text{Diplotene} \rightarrow \text{Diakinesis} \] Descending order means: \[ \text{Latest stage to earliest stage} \]

Step 1: Understanding Zygotene. Zygotene is the stage where:
• Homologous chromosomes pair,
• Synapsis begins. It occurs earlier than: \[ \text{Pachytene, Diplotene, and Diakinesis} \]

Step 2: Understanding Pachytene. Pachytene is characterized by:
• Crossing over,
• Complete synapsis. It occurs after Zygotene.

Step 3: Understanding Diplotene. Diplotene involves:
• Separation of homologous chromosomes,
• Chiasmata visibility. It occurs after Pachytene.

Step 4: Understanding Diakinesis. Diakinesis is the final stage of Prophase-I characterized by:
• Terminalization of chiasmata,
• Maximum chromosome condensation,
• Nuclear membrane disappearance. Thus it is the latest stage among the given options.

Step 5: Writing descending order. Ascending order is: \[ A \rightarrow C \rightarrow D \rightarrow B \] Therefore descending order becomes: \[ B \rightarrow D \rightarrow C \rightarrow A \] Hence, the correct answer is: \[ \boxed{\text{(D) B-D-C-A}} \]