The region of onion root tip, where mitosis occurs, is the apical meristem of the onion root. This is the region of a plant where the fastest cell division and most rapid growth take place.
Mitotic cell division is only visible in actively dividing cells because during this process each new cell requires the same copy of the DNA in the parent cell. The coiled chromosomes during various stages of mitosis in the onion root tip cells can be seen by treating them with DNA specific stains, such as the Feulgen stain.
Mitosis takes many hours to complete. Scientists make slides of cells that are undergoing mitosis to discover specific ones that are in any of the stages of mitosis - prophase, metaphase, anaphase and telophase. During the interphase, which occurs immediately before mitosis, the cell grows a discrete nucleus and nucleoli. The first stage of mitosis is the prophase where the chromatin condenses into different chromosomes and the nuclear envelope splits open to release them into the cytoplasm.
The next stage is the metaphase, where the spindle fastens to the centromere of each pair of chromosome and transfers them to the middle of the cell. The next stage, the anaphase, starts when the chromatids are divided and pulled to the opposite poles. In the final stage, the telophase, the nuclear envelope is transformed, and the chromosomes gradually loosen. Cytokinesis may take place and form a cleavage channel that leads to the separation of the two daughter cells.