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Grey crescent is the area -
A
At the point of entry of sperm into ovum
B
Just opposite to the site of entry of sperm into ovum
C
At the animal pole
D
At the vegetal pole
Detailed Solution
The grey crescent is seen in the fertilised eggs of amphibians such as the frog.
The upper (animal) hemisphere of the egg is pigmented black and the lower (vegetal) hemisphere is yolky and pale.
After the sperm enters, the outer cortical cytoplasm rotates towards the point of sperm entry.
As a result, a crescent-shaped grey area of intermediate pigmentation appears on the side of the egg just opposite to the point of entry of the sperm.
The grey crescent marks the future dorsal side of the embryo; the dorsal lip of the blastopore forms here and it acts as the primary organiser.
So the grey crescent is the area just opposite to the site of entry of the sperm into the ovum.
The upper (animal) hemisphere of the egg is pigmented black and the lower (vegetal) hemisphere is yolky and pale.
After the sperm enters, the outer cortical cytoplasm rotates towards the point of sperm entry.
As a result, a crescent-shaped grey area of intermediate pigmentation appears on the side of the egg just opposite to the point of entry of the sperm.
The grey crescent marks the future dorsal side of the embryo; the dorsal lip of the blastopore forms here and it acts as the primary organiser.
So the grey crescent is the area just opposite to the site of entry of the sperm into the ovum.