FIGURE 19-2 The stages of mitosis. During prophase, the nuclear envelope breaks down, microtubules form the mitotic spindle apparatus, and chromosomes condense. At metaphase, attachment of chromosomes to microtubules via their kinetochores is complete. During anaphase, motor proteins and the shortening of spindle microtubules pull the sister chromatids toward opposite spindle poles. After chromosome movement to the spindle poles, chromosomes decondense. Cells reassemble nuclear membranes around the daughter-cell nuclei and undergo cytokinesis.