Biology (Holt)

Mitosis and Cytokinesis

Although mitosis is a continuous process, biologists traditionally

divide it into four stages, as shown in Figure 9.

Mitosis

Step Prophase Chromosomes coil up and become visible during

prophase. The nuclear envelope dissolves and a spindle forms.

Step MetaphaseDuring metaphase the chromosomes move to the

center of the cell and line up along the equator. Spindle fibers

link the chromatids of each chromosome to opposite poles.

Step Anaphase Centromeres divide during anaphase. The two

chromatids (now called chromosomes) move toward oppo-

site poles as the spindle fibers attached to them shorten.

Step TelophaseA nuclear envelope forms around the chromo-

somes at each pole. Chromosomes, now at opposite poles,

130 CHAPTER 6Chromosomes and Cell Reproduction

BIO

graphic

INTERP

HAS

E

Figure 6-9

Stages of Mitosis

The chromosome copies in the nucleus of a dividing cell are separated into two nuclei.

1 Prophase 2 Metaphase

• Chromosomes
  become visible


• Nuclear envelope
  dissolves


• Spindle forms
  
  
  • Chromosomes
    line up along
    equator
  
  
  
  

Nucleus

Chromosome

(already copied)

Centrioles

Spindle fibers

The chromosomes

replicate during

interphase.

Magnification: 567

G 1

G 2

Mitosis

Cytokinesis

S

Figure 9