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Chapter 8
Cellular Reproduction:
Cells from Cells
PowerPoint® Lectures for
Campbell Essential Biology, Fourth Edition
– Eric Simon, Jane Reece, and Jean Dickey
Campbell Essential Biology with Physiology, Third Edition
– Eric Simon, Jane Reece, and Jean Dickey
Lectures by Chris C. Romero, updated by Edward J. Zalisko
© 2010 Pearson Education, Inc.
WHAT CELL REPRODUCTION
ACCOMPLISHES
• Reproduction:
–
May result in the birth of new organisms
–
More commonly involves the production of new cells
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• When a cell undergoes reproduction, or cell division, two
“daughter” cells are produced that are genetically identical to
each other and to the “parent” cell.
• Before a parent cell splits into two, it duplicates its
chromosomes, the structures that contain most of the organism’s
DNA.
• During cell division, each daughter cell receives one set of
chromosomes.
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• Cell division plays important roles in the lives of organisms.
• Cell division:
– Replaces damaged or lost cells
– Permits growth
– Allows for reproduction
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Human kidney cell
LM
Colorized TEM
FUNCTIONS OF CELL DIVISION
Cell Replacement
Growth via Cell Division
Early human embryo
Figure 8.1a
LM
FUNCTIONS OF CELL DIVISION
Asexual Reproduction
Amoeba
Sea stars
African Violet
Figure 8.1b
• In asexual reproduction, the lone parent and its offspring have
identical genes.
• Mitosis is the type of cell division responsible for:
– Asexual reproduction
– Growth and maintenance of multicellular organisms
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• Sexual reproduction requires fertilization of an egg by a sperm
using a special type of cell division called meiosis.
• Thus, sexually reproducing organisms use:
– Meiosis for reproduction
– Mitosis for growth and maintenance
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Eukaryotic Chromosomes
• Each eukaryotic chromosome contains one very long DNA
molecule, typically bearing thousands of genes.
• The number of chromosomes in a eukaryotic cell depends on the
species.
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Species
Indian muntjac deer
Koala
Opossum
Giraffe
Mouse
Human
Duck-billed platypus
Buffalo
Dog
Red viscacha rat
Number of chromosomes
in body cells
6
16
22
30
40
46
54
60
78
102
Figure 8.2
• Chromosomes:
– Are made of chromatin, a combination of DNA and protein molecules
– Are not visible in a cell until cell division occurs
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• Before a cell divides, it duplicates all of its chromosomes,
resulting in two copies called sister chromatids.
• Sister chromatids are joined together at a narrow “waist” called
the centromere.
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DNA double helix
Histones
TEM
“Beads on
a string”
Nucleosome
Tight helical fiber
Looped domains
TEM
Duplicated chromosomes
(sister chromatids)
Centromere
Figure 8.4
LM
Chromosomes
Figure 8.3
• When the cell divides, the sister chromatids separate from each
other.
• Once separated, each chromatid is:
– Considered a full-fledged chromosome
– Identical to the original chromosome
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Chromosome
duplication
Sister
chromatids
Chromosome
distribution to
daughter cells
Figure 8.5
The Cell Cycle
• A cell cycle is the orderly sequence of events that extend from the
time a cell is first formed from a dividing parent cell to its own
division into two cells.
• The cell cycle consists of two distinct phases:
– Interphase
– The mitotic phase
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• Most of a cell cycle is spent in interphase.
• During interphase, a cell:
– Performs its normal functions
– Doubles everything in its cytoplasm
– Grows in size
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S phase (DNA synthesis;
chromosome duplication)
Interphase: metabolism and
growth (90% of time)
G1
Mitotic (M) phase:
cell division
(10% of time)
Cytokinesis
(division of
cytoplasm)
G2
Mitosis
(division of nucleus)
Figure 8.6
INTERPHASE
Centrosomes
(with centriole pairs)
Chromatin
PROPHASE
Fragments of
Early mitotic
Centrosome nuclear envelope
spindle
Centromere
Spindle
microtubules
LM
Chromosome, consisting
Nuclear Plasma
envelope membrane of two sister chromatids
Figure 8.7.a
METAPHASE
ANAPHASE
TELOPHASE AND CYTOKINESIS
Nuclear
envelope
forming
Spindle
Cleavage
furrow
Daughter
chromosomes
Figure 8.7b
SEM
Cleavage
furrow
Cleavage furrow
Contracting ring of
microfilaments
Daughter cells
Figure 8.8a
Cell plate Daughter
forming nucleus
LM
Wall of
parent cell
Cell wall
Vesicles containing
Cell plate
cell wall material
New cell wall
Daughter cells
Figure 8.8b
Cancer Cells: Growing Out of Control
• Normal plant and animal cells have a cell cycle control system
that consists of specialized proteins, which send “stop” and “goahead” signals at certain key points during the cell cycle.
• Cancer is a disease of the cell cycle.
• Cancer cells do not respond normally to the cell cycle control
system.
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• Cancer cells can form tumors, abnormally growing masses of
body cells.
• The spread of cancer cells beyond their original site of origin is
metastasis.
• Malignant tumors can:
– Spread to other parts of the body
– Interrupt normal body functions
• A person with a malignant tumor is said to have cancer.
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Lymph
vessels
Tumor
Blood
vessel
Glandular
tissue
A tumor grows
from a single
cancer cell.
Cancer cells invade
neighboring tissue.
Metastasis: Cancer
cells spread through
lymph and blood
vessels to other parts
of the body.
Figure 8.9
Cancer Treatment
• Cancer treatment can involve:
– Radiation therapy, which damages DNA and disrupts cell division
– Chemotherapy, which uses drugs that disrupt cell division
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Cancer Prevention and Survival
• Certain behaviors can decrease the risk of cancer:
– Not smoking
– Exercising adequately
– Avoiding exposure to the sun
– Eating a high-fiber, low-fat diet
– Performing self-exams
– Regularly visiting a doctor to identify tumors early
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Meiosis, the Basis of Sexual Reproduction
• Sexual reproduction:
– Uses meiosis
– Uses fertilization
– Produces offspring that contain a unique combination of genes from the
parents (VARIATION)
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Homologous Chromosomes
• Different individuals of a single species have the same number
and types of chromosomes.
• A human somatic cell:
– Is a typical body cell
– Has 46 chromosomes
• Humans have:
– Two different sex chromosomes, X and Y
– Twenty-two pairs of matching chromosomes, called autosomes
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• A karyotype is an image that reveals an orderly arrangement of
chromosomes.
• Homologous chromosomes are matching pairs of chromosomes
that can possess different versions of the same genes.
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LM
Pair of homologous
chromosomes
Centromere
Sister
chromatids
One duplicated
chromosome
Figure 8.11
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• Humans are diploid organisms in which:
– Their somatic cells contain two sets of chromosomes (2n)
– Their gametes are haploid, having only one set of chromosomes (n)
• In humans, a haploid sperm fuses with a haploid egg during
fertilization to form a diploid zygote.
• Sexual life cycles involve an alternation of diploid and haploid
stages.
• Meiosis produces haploid gametes, which keeps the
chromosome number from doubling every generation.
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Haploid gametes (n  23)
Egg cell
n
n
Sperm cell
FERTILIZATION
MEIOSIS
Multicellular
diploid adults
(2n  46)
2n
MITOSIS
and development
Diploid
zygote
(2n  46)
Key
Haploid (n)
Diploid (2n)
Figure 8.12
Chromosomes
duplicate.
Homologous
chromosomes
separate.
Sister
chromatids
separate.
Pair of homologous
chromosomes in
diploid parent cell
Duplicated pair of
homologous
chromosomes
INTERPHASE BEFORE MEIOSIS
Sister
chromatids
MEIOSIS I
MEIOSIS II
Figure 8.13-3
MEIOSIS I: HOMOLOGOUS CHROMOSOMES SEPARATE
INTERPHASE
Centrosomes
(with centriole
pairs)
Nuclear
envelope
Chromatin
Chromosomes
duplicate.
PROPHASE I
Sites of
crossing over
Spindle
Sister
chromatids
Pair of
homologous
chromosomes
Homologous
chromosomes
pair up and
exchange
segments.
METAPHASE I
Microtubules
attached
to chromosome
ANAPHASE I
Sister chromatids
remain attached
Centromere
Pairs of
homologous
chromosomes
line up.
Pairs of
homologous
chromosomes
split up.
Figure 8.14a
PROPHASE I
METAPHASE I
Microtubules attached
Sites of crossing over
to chromosome
Spindle
ANAPHASE I
Sister chromatids
remain attached
TELOPHASE I AND CYTOKINESIS
Cleavage
furrow
Sister
Centromere
chromatids Pair of
homologous
chromosomes
Figure 8.14ab
MEIOSIS II: SISTER CHROMATIDS SEPARATE
TELOPHASE I
AND
CYTOKINESIS
PROPHASE II
METAPHASE II
ANAPHASE II TELOPHASE II
AND
CYTOKINESIS
Cleavage
furrow
Sister
chromatids
separate
Two haploid
cells form;
chromosomes
are still
doubled.
Haploid
daughter
cells forming
During another round of cell division, the sister
chromatids finally separate; four haploid
daughter cells result, containing single
chromosomes.
Figure 8.14b
MEIOSIS
MITOSIS
Prophase I
Prophase
Chromosome
duplication
Duplicated chromosome
(two sister chromatids)
MEIOSIS I
Chromosome
duplication
Parent cell
(before chromosome duplication)
2n  4
Homologous
chromosomes come
together in pairs.
Site of crossing over
between homologous
(nonsister) chromatids
Metaphase I
Metaphase
Homologous pairs
align at the middle
of the cell.
Chromosomes
align at the
middle of the
cell.
Anaphase I
Telophase I
Anaphase
Telophase
2n
Sister
chromatids
separate
during
anaphase.
Daughter cells
of mitosis
2n
Homologous
chromosomes
separate during
anaphase I;
sister chromatids
remain together.
Chromosome with two
sister chromatids
Haploid
n2
Daughter
cells of meiosis I
MEIOSIS II
Sister chromatids
separate during
anaphase II.
n
n
n
Daughter cells of meiosis II
n
Figure 8.15
Independent Assortment of Chromosomes1
POSSIBILITY 2
Metaphase of
meiosis I
Metaphase
of meiosis II
Gametes
Combination a Combination b
Combination c Combination d
Figure 8.16-3
• For any species the total number of chromosome combinations
that can appear in the gametes due to independent assortment is:
– 2n where n is the haploid number.
• For a human:
– n = 23
– 223 = 8,388,608 different chromosome combinations possible in a gamete
© 2010 Pearson Education, Inc.
Random Fertilization
• A human egg cell is fertilized randomly by one sperm, leading to
genetic variety in the zygote.
• If each gamete represents one of 8,388,608 different chromosome
combinations, at fertilization, humans would have 8,388,608 ×
8,388,608, or more than 70 trillion, different possible
chromosome combinations.
© 2010 Pearson Education, Inc.
Crossing Over
• In crossing over:
– Homologous chromosomes exchange genetic information
– Genetic recombination, the production of gene combinations different
from those carried by parental chromosomes, occurs
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Prophase I
of meiosis
Homologous chromatids
exchange corresponding
segments.
Duplicated pair of
homologous
chromosomes
Chiasma, site of
crossing over
Metaphase I
Sister chromatids
remain joined at their
centromeres.
Spindle
microtubule
Metaphase II
Gametes
Recombinant
chromosomes
combine genetic
information from
different parents. Recombinant chromosomes
Figure 8.18-5
Crossing
Over
 During meiosis,
chromosomes cross
over each other
 This allows for
genetic shuffling
and increases
genetic variability
 Offspring have a
unique combination
of genes inherited
from both parents
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When Meiosis Goes Awry
• What happens when errors occur in meiosis?
• Such mistakes can result in genetic abnormalities that range from
mild to fatal.
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How Accidents during Meiosis Can Alter
Chromosome Number
• In nondisjunction, the members of a chromosome pair fail to
separate during anaphase, producing gametes with an incorrect
number of chromosomes.
• Nondisjunction can occur during meiosis I or II.
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NONDISJUNCTION IN MEIOSIS I
NONDISJUNCTION IN MEIOSIS II
Meiosis I
Nondisjunction:
Pair of homologous
chromosomes fails
to separate.
Figure 8.20-1
NONDISJUNCTION IN MEIOSIS II
NONDISJUNCTION IN MEIOSIS I
Meiosis I
Nondisjunction:
Pair of homologous
chromosomes fails
to separate.
Meiosis II
Nondisjunction:
Pair of sister
chromatids
fails to separate.
Gametes
n1
n1
n–1
Abnormal gametes
Number of
n – 1 chromosomes
n1
n–1
Abnormal gametes
n
n
Normal gametes
Figure 8.20-3
• If nondisjunction occurs, and a normal sperm fertilizes an egg
with an extra chromosome, the result is a zygote with a total of
2n + 1 chromosomes.
• If the organism survives, it will have an abnormal number of
genes.
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Abnormal egg
cell with extra
chromosome
n1
Normal
sperm cell
n (normal)
Abnormal zygote
with extra
chromosome 2n  1
Figure 8.21
Down Syndrome: An Extra Chromosome 21
• Down Syndrome:
– Is also called trisomy 21
– Is a condition in which an individual has an extra chromosome 21
– Affects about one out of every 700 children
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LM
Chromosome 21
Figure 8.22
Infants with Down syndrome
(per 1,000 births)
90
80
70
60
50
40
30
20
10
0
20
25
30
35
40
45
50
Age of mother
Figure 8.23
Evolution Connection:
The Advantages of Sex
• Asexual reproduction conveys an evolutionary advantage when
plants are:
– Sparsely distributed
– Superbly suited to a stable environment
• Sexual reproduction may convey an evolutionary advantage by:
– Speeding adaptation to a changing environment
– Allowing a population to more easily rid itself of harmful genes
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Why crossing over is important…
 A male bird with large wings and weak
muscles mated with a female bird with
small wings and strong muscles.
 Describe all the possible characteristics
that could occur in their offspring.
 Would any combination(s) be
advantageous?
 Would any combination(s) be
disadvantageous?
 How could these variations affect the
survival of the organisms?
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LM
(b)
(a)
(c)
(d)
Figure 8.UN6