Section 4: Phases of Mitosis
The mitotic phase can be broken into four stages. The first and longest stage is called prophase. This is where chromatin fibers form chromosomes in the nucleus. Each chromosome consists of a pair of identical chromatids joined at the centromere. The nucleolus disappears and cells stop making ribosomes. A football-shaped structure called the miotic spindle forms, and it pulls chromosomes toward the center of the cell. Metaphase is the second and shortest stage of mitosis. The chromosomes are pulled toward the center of the cell, and spindles connect the centromere of each chromosome to the two poles of the spindles. When the chromosomes line up at the center, anaphase begins. The third stage, anaphase, is where the sister chromatids separate. Each chromatid is considered a “daughter.” Spindles begin to shorten, pulling the split chromatids toward opposite ends or poles of the cell. The result is two identical chromosomes. In the final stage, telophase, chromatids move to opposite sides of the cell and two new nuclei are formed, one on each side of the cell. Two daughter cells are formed when a new double membrane forms, allowing cytoplasm to divide and separate by cytokinesis.