1. Cell Division
MITOSIS & MEIOSIS

3. Interphase
• Stages of Interphase to increase in size. Note that the G
G1 phase: The period prior to the in G2 represents gap and the 2
synthesis of DNA. In this phase, the represents second, so the G2
cell increases in mass in phase is the second gap phase.
preparation for cell division. Note • In the latter part of interphase, the
that the G in G1 represents gap and cell still has nucleoli present.
the 1 represents first, so the G1 • The nucleus is bounded by a
phase is the first gap phase. nuclear envelope and the cell's
• S phase: The period during which chromosomes have duplicated but
DNA is synthesized. In most cells, are in the form of chromatin.
there is a narrow window of time • In animal cells, two pair
during which DNA is synthesized. of centrioles formed from the
Note that the S represents replication of one pair are located
synthesis. outside of the nucleus.
• G2 phase: The period after DNA
synthesis has occurred but prior to
the start of prophase. The cell
synthesizes proteins and continues

4. Prophase

5. Changes that occur in a cell during prophase:
• Chromatin fibers become • In animal cells, the mitotic
coiled into chromosomes with spindle initially appears as
each chromosome having two structures called asters which
chromatids joined at surround each centriole pair.
a centromere.
• The mitotic spindle, composed • The two pair
of microtubules and proteins, f of centrioles (formed from the
orms in the cytoplasm. replication of one pair in
Interphase) move away from
one another toward opposite
ends of the cell due to the
lengthening of the
microtubules that form
between them.

6. In late prophase:
• The nuclear envelope breaks • The kinetochore fibers "interact"
up. with the spindle polar fibers
connecting the kinetochores to
• Polar fibers, which are the polar fibers.
microtubules that make up the
spindle fibers, reach from each • The chromosomes begin to
cell pole to the cell's equator. migrate toward the cell center.
• Kinetochores, which are
specialized regions in the
centromeres of chromosomes,
attach to a type of microtubule
called kinetochore fibers.

7. Metaphase
•The nuclear membrane
disappears completely.
In animal cells, the two
pair of centrioles align at
opposite poles of the
cell.
•Chromosomes move randomly until
•Polar fibers they attach (at their kinetochores) to
(microtubules that make polar fibers from both sides of
up the spindle fibers) their centromeres.
Chromosomes align at the
continue to extend from
metaphase plate at right angles to the
the poles to the spindle poles.
•Chromosomes are held at the
metaphase plate by the equal forces
of the polar fibers pushing on the
centromeres of the chromosomes.

8. Anaphase
•The paired centromeres in
each distinct chromosome
begin to move apart.
•Once the paired sister
chromatids separate from
one another, each is
considered a "full"
chromosome. They are •The daughter chromosomes migrate
referred to as daughter centromere first and
chromosomes. the kinetochore fibers become shorter
as the chromosomes near a pole.
•Through the spindle
apparatus, the daughter •In preparation for telophase, the two
chromosomes move to the cell poles also move further apart during
poles at opposite ends of the course of anaphase. At the end of
the cell. anaphase, each pole contains a
complete compilation of chromosomes.

9. Telophase
• In telophase, the chromosomes
are cordoned off in distinct new
nuclei in the emerging daughter
cells.

11. Interphase
• G1 phase: The period prior to the to increase in size. Note that the G
synthesis of DNA. In this phase, the in G2 represents gap and the 2
cell increases in mass in represents second, so the G2
preparation for cell division. Note phase is the second gap phase.
that the G in G1 represents gap and
the 1 represents first, so the G1 • In the latter part of interphase, the
phase is the first gap phase. cell still has nucleoli present.
• S phase: The period during which • The nucleus is bounded by a
DNA is synthesized. In most cells, nuclear envelope and the cell's
there is a narrow window of time chromosomes have duplicated but
during which DNA is synthesized. are in the form of chromatin.
Note that the S represents
synthesis. • In animal cells, two pair
of centrioles formed from the
• G2 phase: The period after DNA replication of one pair are located
synthesis has occurred but prior to outside of the nucleus.
the start of prophase. The cell
synthesizes proteins and continues

12. Interphase

13. Prophase I:
•Chromosomes thicken and
detach from the nuclear
envelope.
•Similar to mitosis,
•Chromosomes condense the centrioles migrate away
and attach to the nuclear from one another and both
envelope. the nuclear envelope and
nucleoli break down.
•Synapsis occurs (a pair of
•Likewise, the
homologous chromosomes
chromosomes begin their
lines up closely together)
migration to the metaphase
and a tetrad is formed.
plate.
Each tetrad is composed of
four chromatids.
Crossing over may occur.

14. Metaphase I:
•Tetrads align at the
metaphase plate.
•Note that
the centromeres of
homologous
chromosomes are
oriented toward the
opposite cell poles.

15. Anaphase I:
•Chromosomes move to
the opposite cell poles.
Similar to mitosis, the
microtubules and the
kinetochore fibers
interact to cause the
movement.
•Unlike in mitosis, the
homologous
chromosomes move to
opposite poles yet
the sister
chromatids remain
together.

16. Telophase I:
•The spindles continue to
move the homologous
chromosomes to the poles.
Once movement is
complete, each pole has a
haploid number of
chromosomes. •At the end of telophase I and
cytokinesis, two daughter cells are
•In most cases, cytokinesis produced, each with one half the
occurs at the same time as number of chromosomes of the original
telophase I. parent cell.
•Depending on the kind of cell, various
processes occur in preparation for
meiosis II. There is however a
constant: The genetic material does not
replicate again.

17. Prophase II:
•The nuclear membrane and nuclei break up while the spindle
network appears.
•Chromosomes do not replicate any further in this phase of
meiosis.
•The chromosomes begin migrating to the metaphase II plate
(at the cell's equator).

18. Metaphase II:
•The chromosomes line up at
the metaphase II plate at the
cell's center.
•The kinetochores of the
sister chromatids point
toward opposite poles.

19. Anaphase II:
The sister chromatids separate and move toward the
opposite cell poles.

20. Telophase II:
•Distinct nuclei form at the
opposite poles
and cytokinesis occurs.
•At the end of meiosis II, there
are four daughter cells each
with one half the number of
chromosomes of the original
parent cell.

21. Barro, Kevin Winge B.
Casas, Gregorio Jr. A.
CELL DIVISION:
MITOSIS & MEIOSIS