At the end of which phase are chromosomes visible under a microscope?

At the end of prophase, chromosomes become visible under a microscope due to their condensation. During this phase of cell division, the chromatin fibers coil and shorten, making the individual chromosomes distinctly visible. Each chromosome, having already been replicated during the S phase of interphase, consists of two sister chromatids joined at the centromere.

This visibility is critical for the subsequent stages of mitosis where accurate segregation of chromosomes into daughter cells is necessary. In metaphase, chromosomes are aligned at the cell's equatorial plane, and while they remain visible, it is during prophase that their identifiable structure is first apparent. Therefore, the visibility of chromosomes is distinctly attributed to the prophase phase, marking a key transition in the cell division process.