Question

Extrusion of the second polar body from the egg nucleus occurs:

• A. After entry of sperm but before fertilization
• B. After completion of fertilization
• C. Before entry of sperm into the ovum
• D. Simultaneously with first cleavage

Hint:

In humans, meiosis II in the secondary oocyte is completed only after sperm entry, which leads to the formation of the second polar body.

Answer 1

The Correct Option is A

Concept: During oogenesis, the secondary oocyte is arrested in the metaphase stage of meiosis II. Completion of meiosis II occurs only after the sperm enters the ovum.

Step 1: State of the secondary oocyte. At the time of ovulation, the ovum exists as a secondary oocyte and is arrested in metaphase II.

Step 2: Effect of sperm entry. When a sperm enters the secondary oocyte, it triggers the completion of meiosis II.

Step 3: Formation of the second polar body. Completion of meiosis II results in the formation of:
• One mature ovum
• One second polar body

Step 4: Timing of extrusion. Thus, the second polar body is extruded after the entry of sperm but before the completion of fertilization.