MCQ Detailed View

Mitosis is the process by which a eukaryotic cell divides its nucleus, ensuring that each daughter cell receives an identical set of chromosomes. The process occurs in distinct phases: prophase, prometaphase, metaphase, anaphase, and telophase. The first phase, prophase, is when chromosomes become clearly visible under a light microscope for the first time.

In interphase, the stage before mitosis, DNA is loosely organized as chromatin, which cannot be seen as distinct structures under a microscope. When the cell enters prophase, this chromatin begins to condense and coil tightly, forming well-defined chromosomes. Each chromosome is already duplicated during the S phase of interphase, and now consists of two identical sister chromatids joined at a region called the centromere.

During prophase, the nucleolus disappears and the mitotic spindle begins to form from the centrosomes. The nuclear envelope is still intact at this stage, but it will start to break down later, during prometaphase. Because the DNA is condensed and thickened in prophase, this is the first time the chromosomes can be distinctly observed under a light microscope.

In later phases, the chromosomes align at the cell’s equatorial plane (metaphase), separate into individual chromatids (anaphase), and finally, new nuclear envelopes form around the separated groups (telophase). But the initial visibility of chromosomes — the point where students can recognize them under the microscope — happens in prophase.

Recognizing the stages of mitosis is fundamental in biology and cytology, as it explains how cells ensure genetic continuity. The ability to identify chromosomes during prophase provides an essential marker for scientists and students studying cell division under the microscope.