The cell duplicates its DNA and prepares for nuclear division

Stages of mitosis. Only two pairs of chromosomes from a diploid (2n) cell are shown here. The photographs show mitosis in a mouse cell; the DNA is stained blue and the microtubules of the spindle fibers are stained green.

Cell at interphase The cell duplicates its DNA and prepares for nuclear division.

(b) Early prophase
Mitosis begins. The DNA and its associated proteins have started to condense. The two chromosomes color-coded (blue) were inherited from the female parent. The other two (purple) are their counterparts, inherited from the male parent.

(c) Late prophase Chromosomes continue to condense. New spindle fibers become assembled. They move one of the two pairs of centrioles to the opposite end of the cell. The nuclear envelope starts to break down.

(d) Transition to metaphase
Now microtubules penetrate the nuclear region. Collectively, they form a bipolar spindle apparatus. Many of the spindle microtubules become attached to the two sister chromatids of each chromosome.