Grey crescent is the area:

1. at the point of entry of sperm into ovum
2. just opposite to the site of entry of sperm into ovum
3. at the animal pole
4. at the vegetal pole.

Solution

Grey crescent marks the future dorsal side of the embryo. Subsequently, it was determined that the Grey Crescent is formed by the $30^{\circ}$ rotation of the fertilized egg to form a dorsal/ ventral axis. The crescent thus serves as a determinant of dorsal / ventral polarity: cells without it have no means of orientation. Related Theory In the zygote of the frog, there are two poles present. The vegetal pole and the animal pole. These are separated by an area which is rich in melanin and is known as the grey crescent. The egg enters enter opposite to the region of sperm entry. The broadest part of the grey crescent forms the dorsal end. The grey crescent helps in establishing polarity.

Asked in: NEET 2005

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