Question

Which of the following is common to the development of bothbirds and mammals?

(A) holoblastic cleavage

(B) epiblast and hypoblast

(C) trophoblast

(D) gray crescent

Short answer

(A)The option “holoblastic cleavage” is incorrect.

(B)The option “epiblast and hypoblast” is correct.

(C)The option “trophoblast” is incorrect.

(D)The option “gray crescent” is incorrect.

Step-by-step solution

Similarities between birds and mammals

Birds and mammals both belong to vertebrates; both are endothermic, that is, warm-blooded animals. Birds and mammals both possess a four-chambered heart. Just like mammals, birds possess enhanced vocal hearing.

Explanation of option ‘(A)’

Holoblastic cleavage occurs only in mammals and not in birds. In other animals like amphibians, echinoderms, and annelids, holoblastic cleavage occurs. Holoblastic cleavage has a slow rate of division and formation of blastocyst.

Thus, holoblastic cleavage is not common in birds and mammals.

Therefore, the given option is incorrect.

Explanation of option ‘(B)’

The amniote formation in both birds and mammals occurs in the epiblastic and hypoblastic patterns. The epiblast forms the three germ layers: ectoderm, mesoderm, and endoderm. The hypoblast forms the yolk sac.

Thus, hypoblast and epiblast are common in both mammals' and birds' development.

Therefore, the given option is correct.

Explanation of option ‘(C)’

The blastula arranges itself into two layers in mammals, the inner cell mass and the outer trophoblast. The inner cell mass is also known as embryoblast; the cell's mass will form the embryoblast. Trophoblast is not found in a bird’s embryo.

Thus, the trophoblast is not common between both mammals and birds.

Therefore, the given option is incorrect.

Explanation of option ‘(D)’

Gray crescent is an area found in the mammalian egg. The gray crescent forms at the opposite end from where the sperm entered, at the vegetal pole. The gray crescent forms after fertilization.

Thus, the formation of the gray crescent is not common between mammals and birds.

Therefore, the given option is incorrect.