Final answer:
When a cell produces mutated cohesin protein, the cell-cycle event that will be affected is sister chromatid separation.
Step-by-step explanation:
When a cell produces mutated (non-functional) cohesin protein, the cell-cycle event that will be affected is sister chromatid separation (option c).
Cohesin protein plays a crucial role in holding together sister chromatids after DNA replication. During mitosis, cohesin proteins break down to allow the separation of sister chromatids. If the cohesin protein is mutated and non-functional, the sister chromatids will not be able to separate properly.