Which of the Following is Common to the Development of Both

Question

Which of the following is common to the development of both birds and mammals?
A) holoblastic cleavage
B) epiblast and hypoblast
C) trophoblast
D) yolk plug
E) gray crescent

Accepted Answer

Both birds and mammals have an epiblast and hypoblast stage during development where the epiblast cells give rise to the embryo and the hypoblast cells contribute to the formation of the yolk sac. Holoblastic cleavage occurs in some animals but not all, trophoblast is unique to mammals, and the yolk plug and gray crescent are specific to certain types of eggs in different species of animals.