Prophase is the first phase of mitosis. In prophase, chromatin fibers become more tightly coiled and folded, forming discreet chromosomes. The nucleoli disappear and chromosomes appear as two identical sister chromatids joined at the centromere. Mitotic spindles begin to form and with no nuclear envelope, spindles can reach chromosomes. The spindles attach themselves to kinetochores, and move the chromosomes to the center of the cell.