560 Chapter 17 NEL
Interphase
Cells spend most of their lives in interphase. In this phase of the cell cycle, cells are not
actively dividing. Interphase includes the G1, S, and G2 phases of the cell cycle. Cells in
interphase grow and undergo the various metabolic processes needed for their func-
tioning during G1, S, and G2.
Chromosomes are uncondensed throughout interphase (Figure 4). During G1, cells
undergo a period of rapid growth, and the chromosomes are unduplicated. During the
S phase, cells begin to prepare for division during interphase by duplicating its chro-
mosomes. At the end of the S phase, all the chromosomes are therefore duplicated chro-
mosomes. During G2, the cell again grows and it completes the preparations for division
(mitosis, or the M phase).Late Prophase
Chromosomes continue to condense. The
centrioles assemble and spindle fibres attach
to the centromeres of the chromosomes.
The nuclear membrane starts to dissolve.Interphase
The cell replicates its DNA and
prepares for nuclear division.
In humans, each of the
46 chromosomes duplicates
itself. The result is 46 duplicated
chromosomes, or 46 pairs of
chromatids.
Early Prophase
The chromosomes
condense, becoming shorter
and thicker. The centrioles
move to opposite poles of
the cell and spindle fibres
start to form.Figure 4
Interphase and mitosis in an animal cell. Interphase includes the G1, S, and G2 phases of the cell cycle. Mitosis and cytokinesis
occur during the M phase.