Question

Greys crescent is the area:
(a)At the point of entry of sperm into the ovum.
(b)Just opposite to the site of entry of sperm into the ovum
(c)At the animal pole.
(d)At the vegetable pole.

Answer 1

Hint: The greys crescent is the area formed due to changes in the egg due to the entry of the sperm into the egg.

Complete answer:
The Grey region is formed on the ovum due to cytoplasmic movement in the egg which is brought about by the entrance of sperm into the ovum. It is present opposite to the site of entry of the sperm. This grey crescent marks the dorsal side of the embryo when the cell division begins the first cleavage divides this dark crescent into two equal halves. This plane represents the future median plane of the embryo.
The grey crescent materials are present on the dorsal lip of the blastopore in the gastrula stage. The function of the grey crescent is to organize the contents of the embryo if the grey crescent is removed the embryo development is stopped, but it was also seen that when a normal embryo was grafted with an extra grey crescent it developed into two separate embryos.
So, the correct answer is ‘Just opposite to the site of entry of sperm into ovum’

Note: -Amphibian egg contains much more yolk than echinoderm despite the fact that their embryo division is similar, both have holoblastic and radially symmetric embryos.
-The amphibian egg yolk is concentrated in the vegetative hemisphere of the egg.