Phases of Mitosis

Interphase is the first stage of the cell cycle and the period before cell division. During this phase the cell matures and prepares to divide and copies its chromosomes (DNA) and centrioles. Note that centrioles are found only in animal cells.

Each chromosome consists of two identical copies called chromatids. The chromosomes in the nucleus thicken and shorten and the two centrioles move to opposite ends of the cell. Between the centrioles, spindle fibers form at each side of the cell. The nuclear membrane breaks apart.

The double-stranded chromosomes line up along the center of the cell and the spindle fibers attach to each centromere.

The spindle fiber splits the centromere and the chromatids move to opposite sides of the cell.

Nuclear membranes form around each of the two sets of chromatids. The spindle fibers break down and disappear. The chromosomes unwind and the nuclear membrane begins to form around the chromosomes.

Once mitosis is completed, the cytoplasm splits into two. During this stage, the animal cell membrane pinches in at the middle of the cell dividing it into two identical copies of the original cell called daughter cells. Each daughter cell gets half of the cell organelles and an identical set of chromosomes.