Question

Do the data support the hypothesis that the timing of the end of cleavage depends on counting cell divisions? Explain.

Short answer

No, because the toxin’s suppression of cell division does not affect the timing of the cleavage end.

Step-by-step solution

Hypothesis 

The cell cycle during the cleavage stage of the frog embryo comprises only S and M phases. The embryo cells enter the G1 and G2 phase after the 12th cell division, during which the cells grow.

Researchers suggested a hypothesis that the end of cleavage can be determined by counting cell divisions based on this information.

Outline of the experiment

To test the hypothesis, the researchers allowed the frog’s embryo to divide in the presence of radioactively labeled nucleotides such as uridine (for measuring RNA) and thymidine (for measuring DNA).

Then they allowed the embryo to divide in the presence of cytochalasin B, a substance that blocks cleavage furrow development and cytokinesis.

Data does not support the hypothesis

According to the data, the substance that blocks cleavage furrow development and cell division does not affect the cleavage end. As a result, the data does not support the hypothesis.