Three Models for Contractile-Ring Positioning in Animal Cells Are Presented

Short Answer

Three models for contractile-ring positioning in animal cells are presented in the schematic diagrams below. Answer the following question(s) according to these models.

-In experiments on the flattened eggs of the sea urchin Tripneustes gratilla, cytokinesis was analyzed after placing a small physical barrier (e.g. a glass needle or an oil droplet) between the spindle and various areas of the cell cortex. Blocks that were located over the equatorial plane prevented furrow formation in the proximal membrane, whereas blocks located in other areas did not affect furrowing. Which model (1 to 3) is NOT supported by these results? Write down 1, 2, or 3 as your answer.