Chromosomes first become visible during the prophase stage of cell division. This is when the loosely packed chromatin fibers condense into tightly coiled, discrete chromosomes that can be seen under a light microscope.
Details about Prophase and Chromosome Visibility
- Prophase is the initial phase of mitosis (and also meiosis) where the chromatin condenses, making chromosomes visible as distinct structures.
- Each chromosome appears as two sister chromatids joined at the centromere.
- During this phase, the nuclear envelope begins to break down and the mitotic spindle starts to form, setting the stage for chromosome alignment and separation in later phases.
Therefore, the visibility of chromosomes begins at prophase, marking the first phase during which chromosomes can be distinctly seen under a microscope. This applies in both mitosis and meiosis.
