Question

If a sperm nucleus is injected into an oocyte then all of the following events are bypassed except -

• A. The swimming of sperm to meet the egg in the oviduct.
• B. The sperm’s acquisition of motility in the epididymis.
• C. A sperm comes in contact with the zona pellucida layer of the ovum.
• D. The complex process like cell division and cell differentiation.

Hint:

ICSI skips travel, motility and zona contact; embryo growth still needs division and differentiation.

Answer 1

The Correct Option is D

Step 1: Understand the question:
Injecting a sperm nucleus straight into an oocyte is the idea behind ICSI (intracytoplasmic sperm injection).
The sperm is placed inside the egg by hand. So every step that normally brings the sperm to the egg is skipped.
We must find the one event that still has to happen.

Step 2: Check options (A), (B) and (C):
(A) Swimming of the sperm through the female tract to reach the egg is not needed, because the nucleus is placed inside the egg. It is bypassed.
(B) Motility is gained in the epididymis so that sperm can swim later. A bare nucleus does not need to swim. It is bypassed.
(C) Contact with the zona pellucida, the glycoprotein layer around the ovum, never happens when the nucleus is injected inside. It is bypassed.

Step 3: Check option (D):
After the nucleus enters the oocyte, the zygote still has to divide by mitosis (cleavage).
The cells of the embryo then differentiate into tissues and organs. Injection does not replace this process.
So (D) is the event that is not bypassed.

Final Answer:
Option (D), cell division and cell differentiation, is the only event that is not bypassed.
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