The cell-cycle control system initiates chromosome segregation only after which of the following has occurred?

The cell-cycle control system is designed to ensure that the process of cell division occurs accurately and efficiently. One of the critical checkpoints in this control system is the proper alignment of duplicated chromosomes on the mitotic spindle.

When chromosomes are aligned on the spindle, it is known as the metaphase plate, promoting proper segregation during anaphase. The correct alignment of chromosomes is crucial because it guarantees that each daughter cell will receive an identical set of chromosomes, preventing issues such as aneuploidy (abnormal number of chromosomes). The cell-cycle control system monitors this alignment through the spindle assembly checkpoint, which assesses whether all chromosomes are correctly positioned before allowing the separation. This step prevents premature separation and ensures the fidelity of the cell division process.

The other options do not address the direct requirement of chromosome segregation. For instance, the completion of DNA replication is essential, but if the chromosomes are not aligned, segregation cannot occur correctly. Similarly, the cell's growth status and cytokinesis are relevant to cell cycle progression but do not directly influence the initiation of chromosome segregation. It is this careful regulation at the chromosome alignment checkpoint that ensures the integrity of the genomic information passed on to daughter cells.