Final answer:
The classic chromosome structure of DNA becomes visible during prophase of mitosis. If chromosome alignment during metaphase is disrupted, it could cause diseases such as cancer. Nuclear envelope reformation occurs during telophase, and premature reformation could interfere with chromosome segregation.
Step-by-step explanation:
The chromosome structure of DNA becomes visible and assumes its classic appearance during prophase of mitosis. This is when chromosomes condense and become distinguishable with a light microscope. Chromosomes play a critical role in ensuring that DNA is properly copied and distributed to the two daughter cells. If chromosomes did not align during metaphase, it could lead to unequal division of chromosomes, resulting in cells with abnormal numbers of chromosomes, which can cause diseases such as cancer.
The nuclear envelopes reform during telophase, marking the end of the mitotic process. If the nuclear envelopes were to reform prematurely, it could interfere with the correct segregation of chromosomes. Cells spend most of their life in interphase, which is the stage before mitosis begins. The duration of mitosis in a typical eukaryotic cell is relatively short, varying from less than an hour to a few hours, depending on the type of cell and species.