Florida Biology EOC Practice Test

During prophase, the first stage of mitosis, chromosomes become visible as they condense and coil tightly, making them more distinguishable under a microscope. This is when the chromatin, which is loosely arranged DNA, condenses into the distinct structures we know as chromosomes, with each chromosome consisting of two sister chromatids joined at the centromere.

Additionally, at the beginning of prophase, the nuclear membrane starts to break down, allowing the microtubules of the spindle apparatus to access the chromosomes. This breakdown is crucial for the next stages of mitosis, as it enables the separation of chromosomes to occur. The visibility of chromosomes and the breakdown of the nuclear envelope are key characteristics that define prophase within the overall process of cell division.