Question

Grey crescent is
A. Melanin rich area of egg
B. Melanin rich area formed at the region opposite to entry of sperm
C. Yolk rich area of egg
D. Laying of sperms and eggs in frog

Answer 1

Hint:- Grey crescent is a structure formed on the opposite side of sperm entry within the frog egg. It has a bunch of growth factors that basically regulate which part of the cell becomes which part of the body. A cortical area of newly formed embryos of frogs and a few salamanders that forms just after fertilization on the side opposite of sperm penetration.

Complete Answer:- Grey crescent is crescent like and grey in colour developing on the surface of amphibian egg opposite to the point of sperm entry. It is a surface feature developing as a result of cytoplasmic movements stimulated by sperm entry within the egg. Melanin rich area formed at the region opposite to the entry of the sperm. In the zygote of the frog there are two poles present. The vegetal pole and animal pole. These are separated by an area which is rich in melanin and is known as grey crescent.
The egg enters opposite to the area of sperm entry. The broadest part of the grey crescent forms the dorsal end. The grey crescent is ‘melanin rich area formed at the region opposite to the entry of sperm’.
Among animals which produce eggs, yolk is the nutrient-bearing portion of egg whose primary function is to provide food for the development of embryos.

Thus the correct option is B.

Note:- The importance of grey crescent is to mark the future dorsal side of embryo. When the first cleavage happens, the grey crescent is divided into equal halves and this represents the future median plane of the embryo.