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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
• 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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• 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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• 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
• 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
© 2010 Pearson Education, Inc.
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.
• 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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LM
Chromosomes
Figure 8.3
• The DNA in a cell is packed into an elaborate, multilevel system
of coiling and folding.
• Histones are proteins used to package DNA in eukaryotes.
• Nucleosomes consist of DNA wound around histone molecules.
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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
• 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.
• 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
• 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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• The mitotic (M) phase includes two overlapping processes:
– Mitosis, in which the nucleus and its contents divide evenly into two
daughter nuclei
– Cytokinesis, in which the cytoplasm is divided in two
• During mitosis the mitotic spindle, a football-shaped structure of
microtubules, guides the separation of two sets of daughter
chromosomes.
• Spindle microtubules grow from two centrosomes, clouds of
cytoplasmic material that in animal cells contain centrioles.
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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
• Mitosis consists of four distinct phases:
– (A) Prophase
– (B) Metaphase
– (C) Anaphase
– (D) Telophase
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INTERPHASE
Centrosomes
(with centriole pairs)
Chromatin
PROPHASE
Fragments of
Early mitotic
Centrosome nuclear envelope
spindle
Nuclear Plasma
envelope membrane
Chromosome, consisting
of two sister chromatids
Centromere
Spindle
microtubules
Figure 8.7.aa
METAPHASE
ANAPHASE
TELOPHASE AND CYTOKINESIS
Nuclear
envelope
forming
Spindle
Cleavage
furrow
Daughter
chromosomes
Figure 8.7ba
• Cytokinesis typically:
– Occurs during telophase
– Divides the cytoplasm
– Is different in plant and animal cells
© 2010 Pearson Education, Inc.
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
What Is Cancer?
• 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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Meiosis, the Basis of Sexual Reproduction
• Sexual reproduction:
– Uses meiosis
– Uses fertilization
– Produces offspring that contain a unique combination of genes from the
parents
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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
• Humans are diploid organisms in which:
– Their somatic cells contain two sets of chromosomes
– Their gametes are haploid, having only one set of chromosomes
• 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.
© 2010 Pearson Education, Inc.
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
The Process of Meiosis
• In meiosis:
–
Haploid daughter cells are produced in diploid organisms
–
Interphase is followed by two consecutive divisions, meiosis I and
meiosis II
–
Crossing over occurs
© 2010 Pearson Education, Inc.
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
PROPHASE II
ANAPHASE II
TELOPHASE II
AND
CYTOKINESIS
Sister chromatids
separate
Haploid
daughter cells
forming
METAPHASE II
Figure 8.14ba
Review: Comparing Mitosis and Meiosis
• In mitosis and meiosis, the chromosomes duplicate only once,
during the preceding interphase.
• The number of cell divisions varies:
– Mitosis uses one division and produces two diploid cells
– Meiosis uses two divisions and produces four haploid cells
• All the events unique to meiosis occur during meiosis I.
• Offspring of sexual reproduction are genetically different from
their parents and one another.
© 2010 Pearson Education, Inc.
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 Chromosomes
• When aligned during metaphase I of meiosis, the side-by-side
orientation of each homologous pair of chromosomes is a matter
of chance.
• Every chromosome pair orients independently of the others
during meiosis.
© 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.
Figure 8.17
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
© 2010 Pearson Education, Inc.
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
MEIOSIS
MITOSIS
Parent
cell (2n)
Chromosome
duplication
Parent
cell (2n)
Chromosome
duplication
MEIOSIS I
Pairing of
homologous
chromosome
Crossing over
2n
Daughter
cells
2n
MEIOSIS II
n
n
n
n
Daughter cells
Figure 8.UN5