Transcript Slide 1

Chapter 8
The Cellular Basis of Reproduction
and Inheritance
PowerPoint Lectures for
Campbell Biology: Concepts & Connections, Seventh Edition
Reece, Taylor, Simon, and Dickey
© 2012 Pearson Education, Inc.
Lecture by Edward J. Zalisko
Cellular basis of Reproduction and Inheritance
• Why do organisms resemble parents?
 Organisms reproduce their own kind, a key
characteristic of life.
CELL DIVISION AND
REPRODUCTION
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8.1 Cell division plays many important roles in
the lives of organisms
Dividing cells in an
early human
embryo
 Cell division
– Is when one cell gives rise to two cells
– is reproduction at the cellular level,
– requires the duplication of chromosomes, and
– sorts new sets of chromosomes into the resulting pair
of daughter cells.
© 2012 Pearson Education, Inc.
8.1 Cell division plays many important roles in
the lives of organisms
 Cell division is used
– for reproduction of single-celled organisms,
– growth of multicellular organisms from a fertilized egg
into an adult,
– repair and replacement of cells, and
– sperm and egg production.
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8.1 Cell division plays many important roles in
the lives of organisms
 Living organisms reproduce by two methods.
– Asexual reproduction
– produces offspring that are identical to the original cell or
organism and
– involves inheritance of all genes from one parent.
– Sexual reproduction
– produces offspring that are similar to the parents, but show
variations in traits and
– involves inheritance of unique sets of genes from two parents.
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Figure 8.1A
A yeast cell producing a genetically
identical daughter cell
An African violet reproducing
asexually from a cutting (the large
leaf on the left)
Figure 8.1D
Sexual reproduction produces offspring with unique combinations
of genes.
8.2 Prokaryotes reproduce by binary fission
 Prokaryotes (bacteria and archaea) reproduce by
binary fission (“dividing in half”).
 The chromosome of a prokaryote is
– a single circular DNA molecule associated with
proteins and
– much smaller than those of eukaryotes.
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8.2 Prokaryotes reproduce by binary fission
 Binary fission of a prokaryote occurs in three stages:
1. duplication of the chromosome and separation of the
copies,
2. continued elongation of the cell and movement of the
copies, and
3. division into two daughter cells.
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Figure 8.2A_s1
Plasma
membrane
Prokaryotic
chromosome
Cell wall
1
Duplication of the chromosome
and separation of the copies
Figure 8.2A_s2
Plasma
membrane
Prokaryotic
chromosome
Cell wall
1
Duplication of the chromosome
and separation of the copies
2
Continued elongation of the
cell and movement of the copies
Figure 8.2A_s3
Plasma
membrane
Prokaryotic
chromosome
Cell wall
3
1
Duplication of the chromosome
and separation of the copies
2
Continued elongation of the
cell and movement of the copies
Division into
two daughter cells
Figure 8.2B
Prokaryotic chromosomes
THE EUKARYOTIC CELL
CYCLE AND MITOSIS
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8.3 The large, complex chromosomes of
eukaryotes duplicate with each cell division
 Eukaryotic cells
– are more complex and larger than prokaryotic cells,
– have more genes, and
– store most of their genes on multiple linear chromosomes
within the nucleus.
A human kidney cell dividing
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8.3 The large, complex chromosomes of
eukaryotes duplicate with each cell division
 Eukaryotic chromosomes are composed of
chromatin consisting of
– one long DNA molecule and
– histone proteins that
1. help maintain the chromosome structure and
2. control the activity of its genes.
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Figure 8.3A
A plant cell (from an African blood lily) just before
cell division
Figure 8.3B
Chromosomes
DNA molecules
Sister
chromatids
Chromosome
duplication
Centromere
Sister
chromatids
Chromosome
distribution
to the
daughter
cells
8.3 The large, complex chromosomes of
eukaryotes duplicate with each cell division
 Before a eukaryotic cell begins to divide, it
duplicates all of its chromosomes, resulting in
– two copies called sister chromatids
– joined together by a narrowed “waist” called the
centromere.
 When a cell divides, the sister chromatids
– separate from each other, now called chromosomes, and
– sort into separate daughter cells.
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8.3 The large, complex chromosomes of
eukaryotes duplicate with each cell division
 To prepare for division, the chromatin becomes
– highly compact and
– visible with a microscope.
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Figure 8.3B_1
Chromosomes
DNA molecules
Chromosome
duplication
Centromere
Sister
chromatids
Chromosome
distribution
to the
daughter
cells
8.4 The cell cycle multiplies cells
 The cell cycle is an ordered sequence of events
that extends
– from the time a cell is first formed from a dividing
parent cell
– until its own division.
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8.4 The cell cycle multiplies cells
 The cell cycle consists of two stages,
characterized as follows:
1. Interphase: duplication of cell contents
– G1—growth, increase in cytoplasm
– S—duplication of chromosomes
– G2—growth, preparation for division
2. Mitotic phase: division
– Mitosis—division of the nucleus
– Cytokinesis—division of cytoplasm
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Figure 8.4
G1
(first gap)
S
(DNA synthesis)
M
G2
(second gap)
8.5 Cell division is a continuum of dynamic
changes
 Mitosis is unique to eukaryotes
 Mitosis progresses through a series of stages:
– Prophase,
– Prometaphase,
– Metaphase,
– Anaphase, and
– Telophase.
 Cytokinesis often overlaps telophase.
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8.5 Cell division is a continuum of dynamic
changes
 A mitotic spindle is
– required to divide the chromosomes,
– composed of microtubules, and
– produced by centrosomes, structures in the cytoplasm
that
– organize microtubule arrangement and
– contain a pair of centrioles in animal cells.
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Phases in Mitosis
 Prophase
– Chromatin fiber coils into chromosomes; Centriole divides
 Prometaphase
– Chromosomes appear as double structures, each comprising of a pair of sister
chromatids
– Centrioles move to opposite poles; spindle fibers form
 Metaphase
– Chromosomes line up on the metaphase plate of the cell
 Anaphase
– Centromeres split & daughter chromosomes are pulled apart and directed
towards opposite poles
 Telophase
– Daughter nuclei forms at opposite poles and cytoplasm divides by Cytokinesis
8.5 Cell division is a continuum of dynamic
changes
 A mitotic spindle is
– required to divide the chromosomes,
– composed of microtubules, and
– produced by centrosomes, structures in the cytoplasm
that
– organize microtubule arrangement and
– contain a pair of centrioles in animal cells.
Video: Animal Mitosis
Video: Sea Urchin (time lapse)
© 2012 Pearson Education, Inc.
8.5 Cell division is a continuum of dynamic
changes
 Interphase
– The cytoplasmic contents double,
– two centrosomes form,
– chromosomes duplicate in the nucleus during the S
phase, and
– nucleoli, sites of ribosome assembly, are visible.
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Figure 8.5_1
INTERPHASE
Centrosomes
(with centriole pairs)
Centrioles
Nuclear
envelope
Chromatin
Plasma
membrane
MITOSIS
Prophase
Prometaphase
Early mitotic
spindle
Centrosome
Fragments of
the nuclear
envelope
Kinetochore
Centromere
Chromosome,
consisting of two
sister chromatids
Spindle
microtubules
Figure 8.5_left
MITOSIS
INTERPHASE
Prophase
Centrosomes
(with centriole pairs)
Centrioles
Nuclear
envelope
Early mitotic
spindle
Chromatin
Prometaphase
Centrosome
Fragments of
the nuclear envelope
Kinetochore
Plasma
membrane
Centromere
Chromosome,
consisting of two
sister chromatids
Spindle
microtubules
8.5 Cell division is a continuum of dynamic
changes
 Prophase
– In the cytoplasm microtubules begin to emerge from
centrosomes, forming the spindle.
– In the nucleus
– chromosomes coil and become compact and
– nucleoli disappear.
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8.5 Cell division is a continuum of dynamic
changes
 Prometaphase
– Spindle microtubules reach chromosomes, where they
– attach at kinetochores on the centromeres of sister
chromatids and
– move chromosomes to the center of the cell through
associated protein “motors.”
– Other microtubules meet those from the opposite
poles.
– The nuclear envelope disappears.
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Figure 8.5_5
MITOSIS
Anaphase
Metaphase
Metaphase
plate
Mitotic
spindle
Daughter
chromosomes
Telophase and Cytokinesis
Cleavage
furrow
Nuclear
envelope
forming
Figure 8.5_right
MITOSIS
Anaphase
Metaphase
Telophase and Cytokinesis
Metaphase
plate
Cleavage
furrow
Mitotic
spindle
Daughter
chromosomes
Nuclear
envelope
forming
8.5 Cell division is a continuum of dynamic
changes
 Metaphase
– The mitotic spindle is fully formed.
– Chromosomes align at the cell equator.
– Kinetochores of sister chromatids are facing the
opposite poles of the spindle.
– Applying Your Knowledge
By the end of metaphase
–
How many chromosomes are present in one human cell?
–
How many chromatids are present in one human cell?
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8.5 Cell division is a continuum of dynamic
changes
 Anaphase
– Sister chromatids separate at the centromeres.
– Daughter chromosomes are moved to opposite poles
of the cell
– The cell elongates due to lengthening of
nonkinetochore microtubules.
– Applying Your Knowledge
By the end of anaphase
–
–
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How many chromosomes are present in one human cell?
How many chromatids are present in one human cell?
8.5 Cell division is a continuum of dynamic
changes
 Telophase
– The cell continues to elongate.
– The nuclear envelope forms around chromosomes at
each pole, establishing daughter nuclei.
– Chromatin uncoils and nucleoli reappear.
– The spindle disappears.
– Applying Your Knowledge
By the end of telophase
– How many chromosomes are present in one nucleus
within the human cell?
– Are the nuclei identical or different?
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8.5 Cell division is a continuum of dynamic
changes
 Cytokinesis, the cytoplasm is divided into
separate cells.
– Applying Your Knowledge
By the end of cytokinesis
–
How many chromosomes are present in one human cell?
–
How many chromatids are present in one human cell?
–
Do the daughter cells have same number of
chromosomes as the original cell?
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8.6 Cytokinesis differs for plant and animal cells
 In animal cells, cytokinesis occurs as
1. a cleavage furrow forms from a contracting ring of
microfilaments, interacting with myosin, and
2. the cleavage furrow deepens to separate the contents
into two cells.
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Figure 8.6A
Cytokinesis of an animal cell:
Cleavage
furrow
Contracting ring of
microfilaments
Daughter
cells
Cleavage
furrow
8.6 Cytokinesis differs for plant and animal cells
 In plant cells, cytokinesis occurs as
1. a cell plate forms in the middle, from vesicles
containing cell wall material,
2. the cell plate grows outward to reach the edges,
dividing the contents into two cells,
3. each cell now possesses a plasma membrane and cell
wall.
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Figure 8.6B
New
cell wall
Cytokinesis
Cell wall
of the
parent cell
Cell wall
Plasma
membrane
Daughter
nucleus
Cell plate
forming
Vesicles
containing
cell wall
material
Cell plate
Daughter
cells
8.7 Anchorage, cell density, and chemical growth
factors affect cell division
 Factors that control cell division
– the presence of essential nutrients,
– growth factors, proteins that stimulate division. There
are many growth factors. Eg: Endotheilial growth factor,
– density of cells. Crowded cells stop dividing, and this is
known as density-dependent inhibition,
– anchorage. Cells need to be in contact with a solid
surface to divide. This is known as anchorage
dependence.
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Figure 8.7A
Cultured cells
suspended in liquid
The addition of
growth
factor
Figure 8.7B
Anchorage
Single layer
of cells
Removal
of cells
Restoration
of single
layer by cell
division
8.8 Growth factors signal the cell cycle control
system
 The cell cycle control system is a cycling set of
molecules in the cell that
– triggers and
– coordinates key events in the cell cycle.
 Checkpoints in the cell cycle can
– stop an event or
– signal an event to proceed.
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8.8 Growth factors signal the cell cycle control
system
 There are three major checkpoints in the cell cycle.
1. G1 checkpoint
– allows entry into the S phase or
– causes the cell to leave the cycle, entering a nondividing G0
phase.
2. G2 checkpoint, and
3. M checkpoint.
 Research on the control of the cell cycle is one of
the hottest areas in biology today.
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Figure 8.8A
G1 checkpoint
G0
G1
S
Control
system
M
G2
M checkpoint
G2 checkpoint
Figure 8.8B
Growth
factor
EXTRACELLULAR FLUID
Plasma membrane
Relay proteins
Receptor
protein
Signal
transduction
pathway
G1
checkpoint
G1
S
Control
system
M
G2
CYTOPLASM
8.9 CONNECTION: Growing out of control,
cancer cells produce malignant tumors
 Cancer currently claims the lives of 20% of the
people in the United States and other industrialized
nations.
 Cancer is a disease of the cell cycle. Cancer cells
escape controls on the cell cycle.
 Cancer cells
– divide rapidly, often in the absence of growth factors,
– spread to other tissues through the circulatory system, and
– growth is not inhibited by other cells (no density-dependent
inhibition)
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8.9 CONNECTION: Growing out of control,
cancer cells produce malignant tumors
 A tumor is an abnormally growing mass of body
cells.
– Benign tumors remain at the original site.
– Malignant tumors spread to other locations, called
metastasis.
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8.9 CONNECTION: Growing out of control,
cancer cells produce malignant tumors
 Cancers are named according to the organ or
tissue in which they originate.
– Carcinomas arise in external or internal body
coverings.
– Sarcomas arise in supportive and connective tissue.
– Leukemias and lymphomas arise from blood-forming
tissues.
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Figure 8.9
Lymph
vessels
Blood
vessel
Tumor
Tumor in
another
part of
the body
Glandular
tissue
Growth
Invasion
Metastasis
8.9 CONNECTION: Growing out of control,
cancer cells produce malignant tumors
 Cancer treatments
– Localized tumors can be
– removed surgically and/or
– treated with concentrated beams of high-energy radiation.
– Chemotherapy is used for metastatic tumors.
– Chemo drugs inhibit mitosis
– Eg: Vinblastine – inhibits assembly of the spindle
–
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Taxol - prevents disassembly of spindle
8.10 Review: Mitosis provides for growth, cell
replacement, and asexual reproduction
 When the cell cycle operates normally, mitosis
produces genetically identical cells for
– growth,
– replacement of damaged and lost cells, and
– asexual reproduction.
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Figure 8.10A
Figure 8.10B
MEIOSIS AND
CROSSING OVER
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Figure 8.18_s5
Human chromosomes
Centromere
Sister
chromatids
Pair of
homologous
chromosomes
5
Sex chromosomes
8.11 Chromosomes are matched in homologous
pairs
 In humans, somatic cells have 46 chromosomes.
(Somatic cells are all body cells except sperm & eggs)
 Females have – 22 pairs of autosomes and X X
 Males have
– 22 pairs of autosomes and X Y
 Human chromosomes:
 22 pairs of chromosomes are called autosomes.
 X and Y are called sex chromosomes. (X and Y
differ in size and genetic composition)
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8.11 Chromosomes are matched in homologous
pairs
 Pairs of autosomes are called Homologous
chromosomes
 Homologous chromosomes (pairs) are matched in
– length,
– centromere position, and
– gene locations.
 A locus (plural, loci) is the position of a gene.
 Different versions of a gene (called alleles) may be found at the
same locus on maternal and paternal chromosomes.
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Figure 8.11
Pair of homologous
chromosomes
Locus
Centromere
Sister
chromatids
One duplicated
chromosome
8.12 Gametes have a single set of chromosomes
 Egg cells in females and sperm cells in males are
called gametes.
 Human gametes have 23 chromosomes. They are
called haploid cells because they have a single set
of chromosomes.
 All other body cells in humans have 46 chromosomes
and are called diploid cells. These somatic cells have
two sets of chromosomes, one inherited from each
parent.
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8.12 Gametes have a single set of chromosomes
 Meiosis is a process that converts diploid (2n)
nuclei to haploid (n) nuclei.
 Meiosis occurs in the sex organs, producing
gametes—sperm and eggs.
 Fertilization is the union of sperm and egg.
 The zygote has a diploid chromosome number,
one set from each parent.
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Figure 8.12A
Haploid gametes (n  23)
n
Egg cell
n
Sperm cell
Meiosis
Ovary
Fertilization
Testis
Diploid
zygote
(2n  46)
2n
Key
Multicellular diploid
adults (2n  46)
Mitosis
Haploid stage (n)
Diploid stage (2n)
8.12 Gametes have a single set of chromosomes
 All sexual life cycles include an alternation
between
– a diploid stage and
– a haploid stage.
 Producing haploid gametes prevents the
chromosome number from doubling in every
generation.
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8.13 Meiosis reduces the chromosome number
from diploid to haploid
 Meiosis is a type of cell division that produces
haploid gametes in diploid organisms.
 Meiosis (and mitosis) are preceded by the
duplication of chromosomes. However, meiosis is
followed by two consecutive cell divisions.
 Because in meiosis, one duplication of
chromosomes is followed by two divisions, each of
the four daughter cells produced has a haploid set
of chromosomes.
© 2012 Pearson Education, Inc.
Figure 8.12B
How meiosis halves chromosome number
MEIOSIS I
INTERPHASE
MEIOSIS II
Sister
chromatids
2
1
A pair of
homologous
chromosomes
in a diploid
parent cell
A pair of
duplicated
homologous
chromosomes
3
8.13 Meiosis reduces the chromosome number
from diploid to haploid
– Like mitosis, meiosis is preceded by interphase
– Chromosomes duplicate during the S phase
– Unlike mitosis, meiosis has two divisions
– During meiosis I, homologous chromosomes
separate
– The chromosome number is reduced by half
– During meiosis II, sister chromatids separate
– The chromosome number remains the same
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Phases in Meiosis
 Meiosis I
– Prophase I : Synapsis, Chiasma formation & Crossing over
– Metaphase I
– Anaphase I: Homologous chromosomes segregate (tetrad to dyad)
– Telophase I
 Meiosis II
– Prophase II
– Metaphase II
– Anaphase II : Sister chromatids separate (dyad to monad)
– Telophase II
8.13 Meiosis reduces the chromosome number
from diploid to haploid
 Meiosis I – Prophase I
– Chromosomes coil and become compact.
– Homologous chromosomes come together as pairs by
synapsis.
– Each pair, with four chromatids, is called a tetrad.
– Nonsister chromatids exchange genetic material by
crossing over.
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8.13 Meiosis reduces the chromosome number
from diploid to haploid
 Meiosis I – Prophase I
– Applying Your Knowledge
Human cells have 46 chromosomes. At the end of
prophase I
– How many chromosomes are present in one cell?
– How many chromatids are present in one cell?
© 2012 Pearson Education, Inc.
Figure 8.13_left
MEIOSIS I: Homologous chromosomes separate
INTERPHASE:
Chromosomes duplicate
Centrosomes
(with centriole
pairs)
Prophase I
Metaphase I
Sites of crossing over
Spindle microtubules
attached to a kinetochore
Centrioles
Anaphase I
Sister chromatids
remain attached
Spindle
Tetrad
Nuclear
envelope
Chromatin
Sister
chromatids
Fragments
of the
nuclear
envelope
Centromere
(with a
kinetochore)
Metaphase
plate
Homologous
chromosomes
separate
Figure 8.13_1
MEIOSIS I
INTERPHASE:
Chromosomes duplicate
Centrosomes
(with centriole
pairs)
Prophase I
Sites of crossing over
Centrioles
Spindle
Tetrad
Nuclear
envelope
Chromatin
Sister
chromatids
Fragments
of the
nuclear
envelope
Figure 8.13_2
MEIOSIS I
Metaphase I
Spindle microtubules
attached to a kinetochore
Centromere
(with a
kinetochore)
Anaphase I
Sister chromatids
remain attached
Metaphase
plate
Homologous
chromosomes
separate
8.13 Meiosis reduces the chromosome number
from diploid to haploid
 Meiosis I – Metaphase I – Tetrads align at the cell
equator.
 Meiosis I – Anaphase I – Homologous pairs
separate and move toward opposite poles of the cell.
– Applying Your Knowledge
Human cells have 46 chromosomes. At the end of
Metaphase I
– How many chromosomes are present in one cell?
– How many chromatids are present in one cell?
© 2012 Pearson Education, Inc.
8.13 Meiosis reduces the chromosome number
from diploid to haploid
 Meiosis I – Telophase I
– Duplicated chromosomes have reached the poles.
– A nuclear envelope re-forms around chromosomes in
some species.
– Each nucleus has the haploid number of
chromosomes.
– Applying Your Knowledge
After telophase I and cytokinesis
–
How many chromosomes are present in one human
cell?
–
How many chromatids are present in one human cell?
© 2012 Pearson Education, Inc.
8.13 Meiosis reduces the chromosome number
from diploid to haploid
 Meiosis II follows meiosis I without chromosome
duplication.
 Each of the two haploid products enters meiosis II.
 Meiosis II – Prophase II
– Chromosomes coil and become compact (if uncoiled
after telophase I).
– Nuclear envelope, if re-formed, breaks up again.
© 2012 Pearson Education, Inc.
Figure 8.13_right
MEIOSIS II: Sister chromatids separate
Telophase I and Cytokinesis
Prophase II
Metaphase II
Anaphase II
Telophase II
and Cytokinesis
Cleavage
furrow
Sister chromatids
separate
Haploid daughter
cells forming
Figure 8.13_3
Telophase I and Cytokinesis
Cleavage
furrow
Figure 8.13_4
MEIOSIS II: Sister chromatids separate
Prophase II
Metaphase II
Anaphase II
Sister chromatids
separate
Telophase II
and Cytokinesis
Haploid daughter
cells forming
Figure 8.13_5
Two lily cells undergo meiosis II
8.13 Meiosis reduces the chromosome number
from diploid to haploid
 Meiosis II – Metaphase II – Duplicated
chromosomes align at the cell equator.
 Meiosis II – Anaphase II
– Sister chromatids separate and
– chromosomes move toward opposite poles.
© 2012 Pearson Education, Inc.
8.13 Meiosis reduces the chromosome number
from diploid to haploid
 Meiosis II – Telophase II
– Chromosomes have reached the poles of the cell.
– A nuclear envelope forms around each set of
chromosomes.
– With cytokinesis, four haploid cells are produced.
– Applying Your Knowledge
After telophase II and cytokinesis
–
How many chromosomes are present in one human cell?
–
How many chromatids are present in one human cell?
© 2012 Pearson Education, Inc.
8.14 Mitosis and meiosis have important
similarities and differences
 Mitosis and meiosis both
– begin with diploid parent cells that
– have chromosomes duplicated during the previous
interphase.
 However the end products differ.
– Mitosis: two genetically identical cells, with the same
chromosome number as the original cell
– Meiosis: four genetically different cells, with half the
chromosome number of the original cell
– .
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8.15 Mitosis and meiosis have important
similarities and differences
– Which characteristics are unique to meiosis?
– Two divisions of chromosomes
– Pairing of homologous chromosomes
– Exchange of genetic material by crossing over
Copyright © 2009 Pearson Education, Inc.
Figure 8.14
MEIOSIS I
MITOSIS
Parent cell
(before chromosome duplication)
Prophase
Duplicated
chromosome
(two sister
chromatids)
Chromosome
duplication
Site of
crossing
over
Prophase I
Tetrad formed
by synapsis of
homologous
chromosomes
Chromosome
duplication
2n  4
Metaphase I
Metaphase
Chromosomes
align at the
metaphase plate
Tetrads (homologous
pairs) align at the
metaphase plate
Anaphase I
Telophase I
Anaphase
Telophase
Homologous
chromosomes
separate during
anaphase I;
sister
chromatids
remain together
Sister chromatids
separate during
anaphase
Daughter
cells of
meiosis I
MEIOSIS II
2n
2n
Daughter cells of mitosis
No further
chromosomal
duplication;
sister
chromatids
separate during
anaphase II
n
n
n
n
Daughter cells of meiosis II
Haploid
n2
Figure 8.14_1
MEIOSIS I
MITOSIS
Prophase
Parent cell
(before chromosome duplication)
Chromosome
duplication
Prophase I
Site of
crossing
over
Chromosome
duplication
2n  4
Metaphase
Tetrad
Metaphase I
Chromosomes
align at the
metaphase plate
Tetrads (homologous
pairs) align at the
metaphase plate
Figure 8.14_2
MITOSIS
Metaphase
Chromosomes
align at the
metaphase plate
Anaphase
Telophase
Sister chromatids
separate during
anaphase
2n
2n
Daughter cells of mitosis
Figure 8.14_3
MEIOSIS I
Metaphase I
Tetrads (homologous
pairs) align at the
metaphase plate
Anaphase I
Telophase I
Homologous
chromosomes
separate during
anaphase I;
sister
chromatids
remain together
Daughter
cells of
meiosis I
MEIOSIS II
No further
chromosomal
duplication;
sister
chromatids
separate during
anaphase II
n
n
n
n
Daughter cells of meiosis II
Haploid
n2
Figure 8.UN03
Mitosis
Number of chromosomal
duplications
Number of cell divisions
Number of daughter cells
produced
Number of chromosomes in
the daughter cells
How the chromosomes line
up during metaphase
Genetic relationship of the
daughter cells to the parent cell
Functions performed in the
human body
Meiosis
8.15 Independent orientation of chromosomes in
meiosis and random fertilization lead to
varied offspring
 Genetic variation in gametes results from
1. Genetic Recombination
2. Independent orientation at metaphase I
3. Random fertilization
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8.15 Independent orientation of chromosomes in
meiosis and random fertilization lead to
varied offspring
 Genetic Recombination
 Results from crossing over
 More in 8.17
© 2012 Pearson Education, Inc.
8.15 Independent orientation of chromosomes in
meiosis and random fertilization lead to
varied offspring
2. Independent orientation at metaphase I
– Each pair of chromosomes independently aligns at
the cell equator.
– There is an equal probability of the maternal or
paternal chromosome facing a given pole.
– The number of combinations for chromosomes
packaged into gametes is 2n where n = haploid
number of chromosomes.
– How many chromosome combinations can
humans produce?
© 2012 Pearson Education, Inc.
Figure 8.15_s1
Possibility A
Possibility B
Two equally probable
arrangements of
chromosomes at
metaphase I
Figure 8.15_s2
Possibility A
Possibility B
Two equally probable
arrangements of
chromosomes at
metaphase I
Metaphase II
Figure 8.15_s3
Possibility A
Possibility B
Two equally probable
arrangements of
chromosomes at
metaphase I
Metaphase II
Gametes
Combination 1
Combination 2
Combination 3
Combination 4
8.15 Independent orientation of chromosomes in
meiosis and random fertilization lead to
varied offspring
3. Random fertilization
- The combination of each unique sperm with
each unique egg increases genetic variability
– How many possibilities are there when a
unique human egg fertilize with a unique
sperm?
© 2012 Pearson Education, Inc.
8.16 Homologous chromosomes may carry
different versions of genes
 Separation of homologous chromosomes during
meiosis can lead to genetic differences between
gametes.
– Homologous chromosomes may have different versions
of a gene at the same locus.
– One version was inherited from the maternal parent and
the other came from the paternal parent.
– Since homologues move to opposite poles during
anaphase I, gametes will receive either the maternal or
paternal version of the gene.
© 2012 Pearson Education, Inc.
Figure 8.16Q
Sister chromatids
Sister chromatids
Pair of homologous
chromosomes
Figure 8.16
Differing genetic information (coat color and eye color)
on homologous chromosomes
Coat-color
genes
Eye-color
genes
Brown
C
Black
E
Meiosis
c
White
e
Pink
Tetrad in parent cell
(homologous pair of
duplicated chromosomes)
C
E
C
E
c
e
c
e
Chromosomes of
the four gametes
Brown coat (C);
black eyes (E)
White coat (c);
pink eyes (e)
8.17 Crossing over further increases genetic
variability
 Genetic recombination is the production of new
combinations of genes due to crossing over.
 Crossing over is an exchange of corresponding
segments between separate (nonsister)
chromatids on homologous chromosomes.
– Nonsister chromatids join at a chiasma (plural,
chiasmata), the site of attachment and crossing over.
– Corresponding amounts of genetic material are
exchanged between maternal and paternal (nonsister)
chromatids.
© 2012 Pearson Education, Inc.
Figure 8.17B_1
C
E
c
e
1
Breakage of homologous chromatids
C
E
c
e
2
C
Tetrad
(pair of homologous
chromosomes in synapsis)
Joining of homologous chromatids
E
Chiasma
c
e
Figure 8.17B_2
C
E
Chiasma
c
e
3
Separation of homologous
chromosomes at anaphase I
C
E
C
e
c
E
c
e
Figure 8.17B_3
C
E
C
c
e
c
e
E
4
Separation of chromatids at
anaphase II and
completion of meiosis
C
E
C
e
c
E
c
e
Parental type of chromosome
Recombinant chromosome
Recombinant chromosome
Parental type of chromosome
Gametes of four genetic types
ALTERATIONS OF
CHROMOSOME NUMBER
AND STRUCTURE
© 2012 Pearson Education, Inc.
8.18 A karyotype is a photographic inventory of
an individual’s chromosomes
 A karyotype is an ordered display of magnified
images of an individual’s chromosomes arranged
in pairs.
 Karyotypes
– are often produced from dividing cells arrested at
metaphase of mitosis and
– allow for the observation of
– homologous chromosome pairs,
– chromosome number, and
– chromosome structure.
© 2012 Pearson Education, Inc.
Figure 8.18_s3
Packed red
and white
blood cells
Blood
culture
Hypotonic
solution
Centrifuge
2
Fixative
Stain
White
blood
cells
3
Fluid
1
Figure 8.18_s4
4
Figure 8.18_s5
Centromere
Sister
chromatids
Pair of
homologous
chromosomes
5
Sex chromosomes
8.19 CONNECTION: An extra copy of
chromosome 21 causes Down syndrome
 Trisomy 21
– involves the inheritance of three copies of chromosome
21 and
– is the most common human chromosome abnormality.
© 2012 Pearson Education, Inc.
8.19 CONNECTION: An extra copy of
chromosome 21 causes Down syndrome
 Trisomy 21, called Down syndrome, produces a
characteristic set of symptoms, which include:
– mental retardation,
– characteristic facial features,
– short stature,
– heart defects,
– susceptibility to respiratory infections, leukemia, and
Alzheimer’s disease, and
– shortened life span.
 The incidence increases with the age of the mother.
© 2012 Pearson Education, Inc.
Figure 8.19A
Trisomy 21
Figure 8.19B
Infants with Down syndrome
(per 1,000 births)
90
80
70
60
50
40
30
20
10
0
20
25
30
35
40
Age of mother
45
50
8.20 Accidents during meiosis can alter
chromosome number
 Nondisjunction is the failure of chromosomes or
chromatids to separate normally during meiosis.
This can happen during
– meiosis I, if both members of a homologous pair go to
one pole or
– meiosis II if both sister chromatids go to one pole.
 Fertilization after nondisjunction yields zygotes with
altered numbers of chromosomes.
© 2012 Pearson Education, Inc.
Figure 8.20A_s3
MEIOSIS I
Nondisjunction
MEIOSIS II
Normal
meiosis II
Gametes
Number of
chromosomes
n1
n1
n1
Abnormal gametes
n1
Figure 8.20B_s3
MEIOSIS I
Normal
meiosis I
MEIOSIS II
Nondisjunction
n1
n1
Abnormal gametes
n
n
Normal gametes
8.21 CONNECTION: Abnormal numbers of sex
chromosomes do not usually affect survival
 Sex chromosome abnormalities tend to be less
severe, perhaps because of
– the small size of the Y chromosome or
– X-chromosome inactivation.
© 2012 Pearson Education, Inc.
8.21 CONNECTION: Abnormal numbers of sex
chromosomes do not usually affect survival
 The following table lists the most common human
sex chromosome abnormalities. In general,
– a single Y chromosome is enough to produce
“maleness,” even in combination with several X
chromosomes, and
– the absence of a Y chromosome yields “femaleness.”
© 2012 Pearson Education, Inc.
Table 8.21
Kleinfelter Syndrome
47, XXY
Turner Syndrome
45, X
Two kinds of chromosomal aberrations
 Aberrations in chromosome number
 Trisomy 21
 XXY, XYY, XXX, X
 Aberrations in chromosome structure
 Deletions
 Duplications
 Inverstions
 Translocations
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8.23 CONNECTION: Alterations of chromosome
structure can cause birth defects and cancer
 Chromosome breakage can lead to
rearrangements that can produce
– genetic disorders or,
– if changes occur in somatic cells, cancer.
© 2012 Pearson Education, Inc.
8.23 CONNECTION: Alterations of chromosome
structure can cause birth defects and cancer
 These rearrangements may include
– a deletion, the loss of a chromosome segment,
– a duplication, the repeat of a chromosome segment,
– an inversion, the reversal of a chromosome segment,
or
– a translocation, the attachment of a segment to a
nonhomologous chromosome that can be reciprocal.
© 2012 Pearson Education, Inc.
Figure 8.23A_1
Deletion
Duplication
Homologous
chromosomes
Figure 8.23A_2
Inversion
Reciprocal translocation
Nonhomologous
chromosomes
Figure 8.23B
The translocation associated with chronic
myelogenous leukemia
Chromosome 9
Chromosome 22
Reciprocal
translocation
Activated cancer-causing gene
“Philadelphia chromosome”
8.23 CONNECTION: Alterations of chromosome
structure can cause birth defects and cancer
 Chronic myelogenous leukemia (CML)
– is one of the most common leukemias,
– Cancer of white blood cells (leukocytes), and
– Results from part of chromosome 22 switching places with
a small fragment from a tip of chromosome 9.
– The mutated protein turns normal white blood cells to
divide repeatedly, causing leukemia.
– Drug that blocks the action of the abnormal protein is
developed.
– This drug (Gleevac) controls the protein’s activity that
WBCs are no longer produced in an uncontrolled fashion
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