Final answer:
During prophase in mitosis, chromatin compacts into visible chromosomes, with sister chromatids attached at the centromere, and the nuclear envelope breaks down, allowing the chromosomes to be visible under a microscope.
Step-by-step explanation:
During prophase, the chromatin is compacted into visible chromosomes. This stage marks the beginning of mitosis, a process the cell undertakes to replicate and divide. Initially, the chromatin fibers coil and condense with the help of condensin proteins. Subsequently, each chromosome becomes noticeable with its identical partner, known as sister chromatids, which are attached at the centromere, forming an X-shape. The nucleolus vanishes, and the nuclear envelope starts to break down into small vesicles, allowing the chromosomes to become more distinct and visible under a light microscope. These well-coiled sister chromatids are then ready to align during metaphase and are crucial for the accurate genetic division between the two future daughter cells.