During which phase of cell division do chromosomes become visible and the nuclear envelope dissolves?

In the process of cell division, the phase during which chromosomes become visible and the nuclear envelope dissolves is prophase. During this phase, the chromatin condenses into distinct chromosomes, making them easier to see under a microscope. Each chromosome typically consists of two sister chromatids joined at a region called the centromere.

In addition to chromatin condensation, prophase is characterized by the breakdown of the nuclear envelope, allowing the spindle apparatus to interact with the chromosomes. This preparation is crucial for the subsequent phases of mitosis, where the chromosomes need to align and separate properly.

It’s important to note that this visibility and breakdown do not occur in the other phases mentioned. In metaphase, chromosomes are aligned at the cell's equatorial plane; in anaphase, sister chromatids are pulled apart; and during telophase, the chromosomes begin to de-condense, and the nuclear envelope reforms around the separated sets of chromosomes.