Final answer:
Cdc15 yeast mutants grown at a restrictive temperature experience a disruption in cell cycle progression and are unable to complete cytokinesis, resulting in multinucleated cells.
Step-by-step explanation:
When Cdc15 yeast mutants are grown at a restrictive temperature, they experience a disruption in the cell cycle progression. Cdc15 is a protein involved in the regulation of the cell cycle, specifically in the process of cytokinesis. At the restrictive temperature, Cdc15 mutants are unable to properly complete cytokinesis, leading to the accumulation of multinucleated cells.