Page 48 - Demo 1

chromads held together by a structure called the centromere. Chromads
joined together by a centromere are known as sister chromads. Near the end,
the nuclear envelope breaks down and a network of spindle fibers forms in the
cytoplasm. When fully formed, the spindle fibers stretch across the cell.

Figure 27. Stages of Mitosis
Source: http://ib.bioninja.com.au/_Media/mitosis-3_med.jpeg

The metaphase starts when the chromosomes, with spindle fibers aached,
have moved to the equator of the cell. In human cells, at this stage there are
46 centromeres, each aached to two sister chromads.

In the anaphase, the centromeres divide, converng each sister
chromad into a chromosome. Late in this stage, the chromosomes migrate
toward opposite poles and by the end of anaphase, there is a complete set of
chromosomes at each end of the cell.

At the telophase, the chromosomes have reached the opposite ends of
the cell. The chromosomes begin to uncoil, the spindle fibers disintegrate, and
membranes from the ER begin to form a new nuclear envelope to complete
the mitoc phase of the cell cycle.

Cytokinesis takes place toward the end of mitosis. It begins when the
cytoplasm divides and connues aer the nuclei have formed in the daughter
cells. The cell cycle is now complete, and the two daughter cells enter
interphase, during which the cell will grow and DNA will replicate once again.
In animal cells, the first visible sign of cytokinesis is the formaon of a
constricon called a cleavage furrow at the equator of the cell. The constricon
gradually ghtens by the contracon of filaments just under the plasma

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