HUMAN BIOLOGY

CeLL reprOduCtIOn 359

Early prophase
Mitosis begins. In the nucleus, the DNA
begins to condense. The centrosome
gets duplicated.

Prophase
The duplicated chromosomes become
visible as they condense. One of the
two centrosomes moves to the oppo-
site side of the nucleus. The nuclear
envelope breaks up.

Transition to metaphase
The nuclear envelope is gone, and
the chromosomes are at their most
condensed. Spindle microtubules
assemble and bind to chromosomes at
the centromere. Sister chromatids are
attached to opposite spindle poles.

Metaphase
All of the chromosomes are aligned
midway between the spindle poles.

Anaphase
Spindle microtubules separate the sis-
ter chromatids and move them toward
opposite spindle poles. Each sister
chromatid has now become an indi-
vidual, unduplicated chromosome.

Telophase
The chromosomes reach the
spindle poles and decondense.
A nuclear envelope forms around
each cluster, and mitosis ends.

centrosome

microtubule of spindle

1

2

3

4

5

6 Figure 18.6^ Animated!^ Mitosis

ensures that daughter cells will

have the same chromosome

number as the parent cell. For

clarity, the diagram shows only

two pairs of chromosomes from

a diploid (2n) animal cell. (© Cengage

Learning)

All photos: © Michael Clayton, University of Wisconsin

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