During which phase of mitosis do chromosomes line up in the middle of the cell?

During mitosis, chromosomes line up in the center of the cell during metaphase. This phase is characterized by the alignment of chromosomes along the metaphase plate, an imaginary line equidistant from the two spindle poles. The proper alignment is crucial because it ensures that each daughter cell will receive an identical set of chromosomes during the subsequent separation process. The spindle fibers, which are formed during the earlier phases of mitosis, attach to the centromeres of the chromosomes, stabilizing them in preparation for the next phase.

In the other phases: during prophase, chromosomes condense and become visible, but they have not yet lined up. Anaphase is when the sister chromatids are pulled apart toward opposite poles of the cell. Telophase is the final stage, where the separated chromosomes begin to de-condense back into chromatin and nuclear envelopes start to form around each set of chromosomes, further indicating that the chromosomes have already been separated. Thus, the distinct alignment of chromosomes during metaphase is an essential part of ensuring accurate cell division.