During cleavage, the positions of the mitotic spindles
A) determine planes of cleavage.
B) are usually random.
C) are defined by cytoplasmic factors produced during early cleavage stages.
D) are unrelated to the organization of the blastomeres.
E) are similar in radially and spirally cleaving embryos.

Question

Quizplus · Accepted Answer

The positions of the mitotic spindles during cleavage determine the planes of cleavage. This is especially true in radially cleaving embryos where the mitotic spindles are arranged perpendicularly to the animal-vegetal axis, determining the positions of the daughter cells. In spirally cleaving embryos, the mitotic spindles are oriented obliquely, leading to spiral cleavage patterns.

During Cleavage, the Positions of the Mitotic Spindles