PROPHASE: During the prophase the nucleoli in the nucleus disappear. The chromatin fibers become tightly ccoiled and condense into chromosomes. Chromosomes line up in pairs and are joined at the centromere. In the cytoplasm, the spindle fibers begin to form and are made of microtubules. The centrosomes move away from each other, propelled by the lengthening microtubules, or spindle fibers, between them.