Which characterizes development in placental mammals but not birds?
A) Epiblast cells migrate through the primitive groove to become endoderm and mesoderm.
B) The embryo proper forms from the epiblast.
C) The hypoblast contributes to extraembryonic membranes.
D) Signaling molecules in Hensen's node are similar to those found in the frog organizer.
E) Cleavage produces a blastocyst with an inner cell mass.

Question

Quizplus · Accepted Answer

E) Cleavage in placental mammals produces a blastocyst with an inner cell mass, a structure not found in birds. Birds undergo a different type of cleavage and do not form a blastocyst.

Which Characterizes Development in Placental Mammals but Not Birds