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Chapter 8
Cell Division
and
Reproduction
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Cell Division Ensures
the Passage of
Genetic Information
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8.1 Cell division is involved
in both asexual and
sexual reproduction
 Somatic cells - body cells make up most of the
organism
 Asexual reproduction - increase in number of
somatic cells or the number unicellular organisms
 Germ cells - found only in testes and ovaries,
they produce sperm or eggs
 Sexual reproduction – requires the production of
eggs and sperm
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8.2 Prokaryotes reproduce
asexually
 In bacteria and archaea, reproduction consists
of duplicating the single chromosome, located in
the nucleoid, and distributing a copy to each
daughter cell
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Figure 8.2 Prokaryotes use binary fission to reproduce
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Somatic Cells Have a Cell Cycle
and Undergo Mitosis
and Cytokinesis
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8.3 The eukaryotic cell cycle
is a set series of events
 Interphase - the time when a cell performs its
usual functions
Figure 8.3A Stages of the cell cycle.
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M (Mitotic) Stage
 Cell division occurs during the M stage
and encompasses both division of the
nucleus and division of the cytoplasm
 Mitosis - nuclear division in the cell cycle
 Cytokinesis - division of the cytoplasm
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Figure 8.3B Cytokinesis is a noticeable part of the cell cycle
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8.4 Eukaryotic chromosomes are
visible during cell division
 When a eukaryotic cell is not undergoing
division, the DNA within a chromosome is a
mass of thin threads called chromatin
 Before nuclear division chromatin condenses,
 2 identical chromatids are sister chromatids
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Figure 8.4A A condensed duplicated chromosome
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Somatic Cells Are Diploid (2n)
 Diploid (2n) - includes two chromosomes of
each kind
 During mitosis, a 2n nucleus divides to produce
daughter nuclei that are also 2n
 A dividing cell is called the parent cell and the new
cells are called the daughter cells
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Gametes Are Haploid (n)
 Haploid (n) number of chromosomes, contains
only one chromosome of each kind
 Half the diploid number
Figure 8.4B When sister chromatids separate, each daughter
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nucleus gets a chromosome
8.5 Mitosis maintains the
chromosome number
 Before mitosis, DNA has replicated, each double
helix is in a chromatid and the chromosomes
consist of sister chromatids attached at a
centromere
 The centrosome - the microtubule-organizing center
of the cell divides before mitosis
 Spindle fibers separate the sister chromatids of the
duplicated chromosomes
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Figure 8.5 Phases of mitosis in animal cells and plant cells
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Figure 8.5 Phases of mitosis in animal cells and plant cells
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8.6 Cytokinesis divides
the cytoplasm
 Cytokinesis follows mitosis in most cells
 Cytokinesis in plant cells occurs by a process
different than in animal cells
 Cell plate - newly formed plasma membrane that
expands outward
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Figure 8.6A Cytokinesis in an animal cell
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Figure 8.6B Cytokinesis in plant cells
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Cancer Is Uncontrolled
Cell Division
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8.7 Cell cycle control occurs
at checkpoints
 The cell cycle has checkpoints that can
delay the cell cycle until all is well
 Apoptosis - programmed cell death
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Figure 8.7 Cell cycle checkpoints
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8.8 Signals affect the cell cycle
control system
 Signaling molecules stimulate or inhibit
 Kinases remove phosphate from ATP and add it
to another molecule
 Cyclins combine with kinases
 Control system for cell division control whether
kinases and cyclins are present
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Figure 8.8A Internal signals of the cell cycle are kinases and cyclins
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Figure 8.8B A cell-signaling pathway activates the control system
to produce kinases and cyclins
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Cell Cycle Inhibition
 Contact Inhibition - In a culture, cells divide
until they line a container in a sheet and then
stop dividing
 Cells “remember” number of divisions
 Telomere - repeating DNA base sequence
 Each time a cell divides some portion of a telomere is
lost
 When telomeres become too short, chromosomes
fuse and do not duplicate
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8.9 Cancer cells have
abnormal characteristics
 A mutation (a DNA change) causes a cell to divide
uncontrollably or ignore apoptosis
 Carcinogenesis - development of cancer
 Characteristics of cancer cells
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
Lack differentiation
Have abnormal nuclei
Form tumors
Metastasis - establishing new tumors
Angiogenesis - formation of new blood vessels
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Figure 8.9
Development of
breast cancer
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APPLYING THE CONCEPTS—HOW BIOLOGY IMPACTS OUR LIVES
8.10 Protective behaviors and
diet help prevent cancer
 Behaviors that help prevent cancer

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


Don’t smoke
Use sunscreen
Avoid radiation
Be tested for cancer
Be aware of occupational hazards
Carefully consider hormone therapy
 Dietary guidelines to reduce cancer risk

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Increase consumption of foods rich in vitamins A and C
Limit consumption of salt-cured, smoked, or nitrite-cured foods
Include vegetables from the cabbage family
Be moderate in the consumption of alcohol
Maintain a healthy weight
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Meiosis Produces Cells That
Become the Gametes in Animals
and Spores in Other Organisms
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8.11 Homologous chromosomes
separate during meiosis
 Karyotype - picture of chromosomes in
numbered pairs called homologous
chromosomes or homologues
 X and Y chromosomes are the sex chromosomes
because they contain the genes that determine
gender
 Autosomes - all the pairs of chromosomes except the sex
chromosomes
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Figure 8.11 A karyotype shows that the chromosomes
occur as pairs
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Meiosis
 Occurs during the production of the sperm and
egg
 Requires two divisions
 Meiosis I - the chromosomes of each homologous
pair separate
 Meiosis II - the sister chromatids of each duplicated
chromosome separate
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8.12 Synapsis and crossing-over
occur during meiosis I
 Synapsis - homologous chromosomes come
together and line up side by side forming a
tetrad
 Crossing-over - during synapsis, nonsister
chromatids exchange genetic material
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Figure 8.12A Synapsis of homologues
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Figure 8.12B
Crossing-over
of nonsister
chromatids
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8.13 Sexual reproduction
increases genetic variation
 Fertilization, the union of a male and a female
gamete, enhances genetic variation
 Sexual reproduction brings about genetic variation,
and some offspring may have a better chance of
survival and reproductive success than others
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Figure 8.13 Independent assortment increases genetic variation
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8.14 Meiosis requires two
division cycles
 Prophase, metaphase, anaphase, and
telophase occur during both meiosis I and
meiosis II
 No replication of DNA occurs during a period
called interkinesis between meiosis I and II
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Figure 8.14A Phases of meiosis I
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Figure 8.14A Phases of meiosis I
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Figure 8.14B Phases of meiosis II
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Figure 8.14B Phases of meiosis II
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8.15 The life cycle of most
multicellular organisms
includes both mitosis and meiosis
 Life cycle - in sexually reproducing organisms, all
the reproductive events from one generation to
the next
 Spermatogenesis in males, occurs in the testes and
produces sperm
 Oogenesis in females, occurs in the ovaries and
produces eggs
 Zygote - product of the sperm and egg joining
during fertilization, has homologous pairs of
chromosomes
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Figure 8.15A
Life cycle of
humans
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Figure 8.15B Life cycle of plants
Figure 8.15C Life cycle of algae
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8.16 Meiosis can be compared to mitosis
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Chromosomal Abnormalities
Can Be Inherited
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8.17 An abnormal chromosome
number is sometimes traceable
to nondisjunction
 Polyploidy - a eukaryote has three or more complete
sets of chromosomes
 Aneuploidy - an organism has more or less than the
normal number of chromosomes
 Monosomy only one of a type of chromosome
 Trisomy three of a type of chromosome
 Nondisjunction - in meiosis I homologues do not
separate and both go into the same daughter cell, or in
meiosis II sister chromatids fail to separate and both
daughter chromosomes go to the same gamete
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Figure 8.17A Nondisjunction of chromosomes during
meiosis I of oogenesis, followed by fertilization with
normal sperm
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Figure 8.17B Nondisjunction of chromosomes during
meiosis II of oogenesis, followed by fertilization with
normal sperm
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8.18 Abnormal chromosome
numbers cause syndromes
 Trisomy 21 (Down Syndrome)
 Over 90% of individuals with Down syndrome have three
copies of chromosome 21
 Abnormal Sex Chromosome Inheritance
 Turner syndrome females are born with only a single X
chromosome
 A male with Klinefelter syndrome has two or more X
chromosomes in addition to a Y chromosome
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8.19 Abnormal chromosome
structure also causes syndromes
 Various agents in the environment, such as
radiation, certain organic chemicals, or viruses,
can cause chromosomes to break
 Deletion - an end of a chromosome breaks off or two
simultaneous breaks lead to the loss of an internal
segment
 Duplication - the presence of a particular
chromosome segment more than once in the same
chromosome
 Inversion - a segment of a chromosome is turned
180 degrees
 Translocation - the movement of a chromosome
segment from one chromosome to another
nonhomologous chromosome
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Figure 8.19
Types of
chromosomal
mutations
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Connecting the Concepts:
Chapter 8
 All cells receive DNA from preexisting cells
through the process of cell division
 Mitosis is part of the cell cycle, and there are negative
consequences if the cell cycle comes out of
synchronization
 Meiosis is part of the production of gametes, which
have half the number of chromosomes as the parent
cell
 Sexual reproduction increases genetic variability
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