The prophase

      The duplicated chromosomes are prepared for segregation, and the mitotic machinery is assembled.

• Chromosomal material condenses to form compact mitotic chromosomes

 

• Chromosomes composed of two chromatids attached together at the centromere

 

• Mitotic spindle is assembled

The microtubules of the cytoskeleton undergo sweeping disassembly in preparation for their reassembly to form the components of the microtubule-containing “machine” called the mitotic spindle. The first stage in spindle formation is the appearance of the microtubules in a “sunburst” arrangement, or aster, around each centrosome during early prophase. The process of aster formation is followed by separation of the centrosomes from one another and the subsequent migration around the nucleus toward opposites sides of the cell. As the pairs of centrioles separate, the microtubules stretching between them increase in number and elongate. Eventually, the two centrosomes reach points opposite to one another, thus establishing the two poles of the mitotic spindle.

 

• Cytoskeleton and nuclear envelope disappear. ER fragment.