chapter 8 the cellular basis of reproduction · pdf filechapter 8: big ideas cell division and...
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© 2012 Pearson Education, Inc. Lecture by Edward J. Zalisko
PowerPoint Lectures for
Campbell Biology: Concepts & Connections, Seventh EditionReece, Taylor, Simon, and Dickey
Chapter 8 The Cellular Basis of Reproduction and Inheritance
Cancer cells
– start out as normal body cells,
– undergo genetic mutations,
– lose the ability to control the tempo of their own division, and
– run amok, causing disease.
Introduction
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In a healthy body, cell division allows for
– growth,
– the replacement of damaged cells, and
– development from an embryo into an adult.
In sexually reproducing organisms, eggs and sperm result from
– mitosis and
– meiosis.
Introduction
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Figure 8.0_1
Figure 8.0_2Chapter 8: Big Ideas
Cell Division andReproduction
The Eukaryotic CellCycle and Mitosis
Meiosis andCrossing Over
Alterations of ChromosomeNumber and Structure
Figure 8.0_3
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CELL DIVISION AND REPRODUCTION
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8.1 Cell division plays many important roles in the lives of organisms
Organisms reproduce their own kind, a key characteristic of life.
Cell division
– is reproduction at the cellular level,
– requires the duplication of chromosomes, and
– sorts new sets of chromosomes into the resulting pair of daughter cells.
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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.
8.1 Cell division plays many important roles in the lives of organisms
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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 Figure 8.1B
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Figure 8.1C Figure 8.1D
Figure 8.1E Figure 8.1F
Prokaryotes (bacteria and archaea) reproduce by binary fission (“dividing in half”).
The chromosome of a prokaryote is
– a singular circular DNA molecule associated with proteins and
– much smaller than those of eukaryotes.
8.2 Prokaryotes reproduce by binary fission
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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.
8.2 Prokaryotes reproduce by binary fission
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Figure 8.2A_s1
Plasmamembrane
Cell wall
Duplication of the chromosomeand separation of the copies
Prokaryoticchromosome
1
Figure 8.2A_s2
Plasmamembrane
Cell wall
Duplication of the chromosomeand separation of the copies
Continued elongation of thecell and movement of the copies
Prokaryoticchromosome
1
2
Figure 8.2A_s3
Plasmamembrane
Cell wall
Duplication of the chromosomeand separation of the copies
Continued elongation of thecell and movement of the copies
Prokaryoticchromosome
1
2
3Division into
two daughter cells
Figure 8.2B
Prokaryotic chromosomes
THE EUKARYOTIC CELL CYCLE AND MITOSIS
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Eukaryotic cells
– are more complex and larger than prokaryotic cells,
– have more genes, and
– store most of their genes on multiple chromosomes within the nucleus.
8.3 The large, complex chromosomes of eukaryotes duplicate with each cell division
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Eukaryotic chromosomes are composed of chromatin consisting of
– one long DNA molecule and
– proteins that help maintain the chromosome structure and control the activity of its genes.
To prepare for division, the chromatin becomes
– highly compact and
– visible with a microscope.
8.3 The large, complex chromosomes of eukaryotes duplicate with each cell division
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Figure 8.3A
Figure 8.3B
Sisterchromatids
Chromosomes
Centromere
Chromosomeduplication
Sisterchromatids
Chromosomedistribution
to thedaughter
cells
DNA moleculesFigure 8.3B_2
Sisterchromatids
Centromere
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.
8.3 The large, complex chromosomes of eukaryotes duplicate with each cell division
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Figure 8.3B_1Chromosomes
Centromere
Chromosomeduplication
Sisterchromatids
Chromosomedistribution
to thedaughter
cells
DNA molecules
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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.
8.4 The cell cycle multiplies cells
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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
8.4 The cell cycle multiplies cells
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Figure 8.4
G1(first gap)
S(DNA synthesis)
G2
(second gap)
M
Mitosis progresses through a series of stages:
– prophase,
– prometaphase,
– metaphase,
– anaphase, and
– telophase.
Cytokinesis often overlaps telophase.
8.5 Cell division is a continuum of dynamic changes
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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.
8.5 Cell division is a continuum of dynamic changes
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Video: Sea Urchin (time lapse)
Video: Animal Mitosis
Figure 8.5_1
INTERPHASEMITOSIS
Prophase Prometaphase
Centrosome
Early mitoticspindle
Chromatin
Fragments ofthe nuclearenvelope
Kinetochore
Centrosomes(with centriole pairs)
Centrioles
Nuclearenvelope
Plasmamembrane
Chromosome,consisting of twosister chromatids
CentromereSpindlemicrotubules
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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.
8.5 Cell division is a continuum of dynamic changes
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Figure 8.5_2
INTERPHASE
Figure 8.5_left
INTERPHASEMITOSIS
Prophase Prometaphase
CentrosomeEarly mitoticspindle
Chromatin
Fragments ofthe nuclear envelope
Kinetochore
Centrosomes(with centriole pairs)
Centrioles
Nuclearenvelope
Plasmamembrane
Chromosome,consisting of twosister chromatids
Centromere Spindlemicrotubules
Prophase
– In the cytoplasm microtubules begin to emerge from centrosomes, forming the spindle.
– In the nucleus
– chromosomes coil and become compact and
– nucleoli disappear.
8.5 Cell division is a continuum of dynamic changes
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Figure 8.5_3
Prophase
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.
8.5 Cell division is a continuum of dynamic changes
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Figure 8.5_4
Prometaphase
Figure 8.5_5
MITOSIS
AnaphaseMetaphase Telophase and Cytokinesis
Metaphaseplate Cleavage
furrow
NuclearenvelopeformingDaughter
chromosomesMitoticspindle
Figure 8.5_right
MITOSIS
AnaphaseMetaphase Telophase and Cytokinesis
Metaphaseplate
Cleavagefurrow
Nuclearenvelopeforming
Daughterchromosomes
Mitoticspindle
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.
8.5 Cell division is a continuum of dynamic changes
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Figure 8.5_6
Metaphase
Anaphase – Sister chromatids separate at the centromeres.
– Daughter chromosomes are moved to opposite poles of the cell as
– motor proteins move the chromosomes along the spindle microtubules and
– kinetochore microtubules shorten.
– The cell elongates due to lengthening of nonkinetochore microtubules.
8.5 Cell division is a continuum of dynamic changes
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Figure 8.5_7
Anaphase
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.
8.5 Cell division is a continuum of dynamic changes
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Figure 8.5_8
Telophase and Cytokinesis
During cytokinesis, the cytoplasm is divided into separate cells.
The process of cytokinesis differs in animal and plant cells.
8.5 Cell division is a continuum of dynamic changes
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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.
8.6 Cytokinesis differs for plant and animal cells
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Figure 8.6A
Cytokinesis
Cleavagefurrow Contracting ring of
microfilaments
Daughtercells
Cleavagefurrow
10
Figure 8.6A_1
Cleavagefurrow
Figure 8.6A_2
Cleavagefurrow Contracting ring of
microfilaments
Daughtercells
In plant cells, cytokinesis occurs as1. 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.
8.6 Cytokinesis differs for plant and animal cells
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Animation: Cytokinesis
Figure 8.6B
Cytokinesis
Cell wallof theparent cell
Daughternucleus
Cell wall
Plasmamembrane
Vesiclescontainingcell wallmaterial
Cell plateforming
Newcell wall
Cell plate Daughtercells
Figure 8.6B_1
Cell wallof theparent cell
Daughternucleus
Cell plateforming
Figure 8.6B_2
Cell wall
Plasmamembrane
Vesiclescontainingcell wallmaterial
Newcell wall
Cell plate Daughtercells
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The cells within an organism’s body divide and develop at different rates.
Cell division is controlled by
– the presence of essential nutrients,
– growth factors, proteins that stimulate division,
– density-dependent inhibition, in which crowded cells stop dividing, and
– anchorage dependence, the need for cells to be in contact with a solid surface to divide.
8.7 Anchorage, cell density, and chemical growthfactors affect cell division
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Figure 8.7A
Cultured cellssuspended in liquid
The addition ofgrowthfactor
Figure 8.7B
Anchorage
Single layerof cells
Removalof cells
Restorationof singlelayer by celldivision
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.
8.8 Growth factors signal the cell cycle control system
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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.
8.8 Growth factors signal the cell cycle control system
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Figure 8.8A
G0
G1 checkpoint
G1S
M
G2
Controlsystem
M checkpoint
G2 checkpoint
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Figure 8.8B
Receptorprotein
Signaltransductionpathway
Growthfactor
Relay proteins
Plasma membraneEXTRACELLULAR FLUID
CYTOPLASM
G1checkpoint
G1S
M
G2
Controlsystem
Cancer currently claims the lives of 20% of the people in the United States and other industrialized nations.
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
– grow without being inhibited by other cells.
8.9 CONNECTION: Growing out of control, cancer cells produce malignant tumors
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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.
8.9 CONNECTION: Growing out of control, cancer cells produce malignant tumors
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Figure 8.9
Tumor
Glandulartissue
Growth Invasion Metastasis
Lymphvessels
Bloodvessel
Tumor inanotherpart of the body
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.
8.9 CONNECTION: Growing out of control, cancer cells produce malignant tumors
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Cancer treatments
– Localized tumors can be
– removed surgically and/or
– treated with concentrated beams of high-energy radiation.
– Chemotherapy is used for metastatic tumors.
8.9 CONNECTION: Growing out of control, cancer cells produce malignant tumors
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When the cell cycle operates normally, mitosis produces genetically identical cells for
– growth,
– replacement of damaged and lost cells, and
– asexual reproduction.
8.10 Review: Mitosis provides for growth, cell replacement, and asexual reproduction
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Video: Hydra Budding
Figure 8.10A
Figure 8.10A_1 Figure 8.10B
Figure 8.10C
MEIOSIS AND CROSSING OVER
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In humans, somatic cells have
– 23 pairs of homologous chromosomes and
– one member of each pair from each parent.
The human sex chromosomes X and Y differ in size and genetic composition.
The other 22 pairs of chromosomes are autosomes with the same size and genetic composition.
8.11 Chromosomes are matched in homologous pairs
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Homologous chromosomes are matched in
– length,
– centromere position, and
– gene locations.
A locus (plural, loci) is the position of a gene.
Different versions of a gene may be found at the same locus on maternal and paternal chromosomes.
8.11 Chromosomes are matched in homologous pairs
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Figure 8.11
Pair of homologouschromosomes
Locus
Centromere
Sisterchromatids
One duplicatedchromosome
An organism’s life cycle is the sequence of stages leading
– from the adults of one generation
– to the adults of the next.
Humans and many animals and plants are diploid, with body cells that have
– two sets of chromosomes,
– one from each parent.
8.12 Gametes have a single set of chromosomes
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Meiosis is a process that converts diploid nuclei to haploid nuclei.
– Diploid cells have two homologous sets of chromosomes.
– Haploid cells have one set of chromosomes.
– 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.
8.12 Gametes have a single set of chromosomes
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Figure 8.12AHaploid gametes (n 23)
Egg cell
Sperm cell
Fertilization
n
n
Meiosis
Ovary Testis
Diploidzygote(2n 46)
2n
MitosisKey
Haploid stage (n)Diploid stage (2n)
Multicellular diploidadults (2n 46)
15
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.
8.12 Gametes have a single set of chromosomes
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Figure 8.12B
A pair ofhomologouschromosomesin a diploidparent cell
A pair ofduplicatedhomologouschromosomes
Sisterchromatids
1 2 3
INTERPHASE MEIOSIS I MEIOSIS II
Meiosis is a type of cell division that produces haploid gametes in diploid organisms.
Two haploid gametes combine in fertilization to restore the diploid state in the zygote.
8.13 Meiosis reduces the chromosome number from diploid to haploid
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Meiosis and mitosis are preceded by the duplication of chromosomes. However,
– meiosis is followed by two consecutive cell divisions and
– mitosis is followed by only one cell division.
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.
8.13 Meiosis reduces the chromosome number from diploid to haploid
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Meiosis I – Prophase I – events occurring in the nucleus.
– 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.
8.13 Meiosis reduces the chromosome number from diploid to haploid
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Figure 8.13_left
Centrosomes(with centriolepairs) Centrioles
Sites of crossing over
Spindle
Tetrad
Nuclearenvelope
Chromatin Sisterchromatids Fragments
of thenuclearenvelope
Centromere(with akinetochore)
Spindle microtubulesattached to a kinetochore
Metaphaseplate Homologous
chromosomesseparate
Sister chromatidsremain attached
Chromosomes duplicate Prophase I Metaphase I Anaphase IINTERPHASE:
MEIOSIS I: Homologous chromosomes separate
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Figure 8.13_1
Centrosomes(with centriolepairs) Centrioles
Sites of crossing over
Spindle
Tetrad
Nuclearenvelope
Chromatin Sisterchromatids Fragments
of thenuclearenvelope
Chromosomes duplicate Prophase IINTERPHASE:
MEIOSIS I
Figure 8.13_2
Centromere(with akinetochore)
Spindle microtubulesattached to a kinetochore
Metaphaseplate Homologous
chromosomesseparate
Sister chromatidsremain attached
Metaphase I Anaphase I
MEIOSIS I
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.
8.13 Meiosis reduces the chromosome number from diploid to haploid
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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.
8.13 Meiosis reduces the chromosome number from diploid to haploid
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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.
8.13 Meiosis reduces the chromosome number from diploid to haploid
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Figure 8.13_right
Cleavagefurrow
Telophase I and Cytokinesis Prophase II Metaphase II Anaphase II
MEIOSIS II: Sister chromatids separate
Sister chromatidsseparate
Haploid daughtercells forming
Telophase IIand Cytokinesis
17
Figure 8.13_3
Cleavagefurrow
Telophase I and Cytokinesis
Figure 8.13_4
Prophase II Metaphase II Anaphase II
MEIOSIS II: Sister chromatids separate
Sister chromatidsseparate
Haploid daughtercells forming
Telophase IIand Cytokinesis
Figure 8.13_5
Two lily cellsundergo meiosis II
Meiosis II – Metaphase II – Duplicated chromosomes align at the cell equator.
Meiosis II – Anaphase II
– Sister chromatids separate and
– chromosomes move toward opposite poles.
8.13 Meiosis reduces the chromosome number from diploid to haploid
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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.
8.13 Meiosis reduces the chromosome number from diploid to haploid
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Mitosis and meiosis both
– begin with diploid parent cells that
– have chromosomes duplicated during the previous interphase.
However the end products differ.
– Mitosis produces two genetically identical diploid somatic daughter cells.
– Meiosis produces four genetically unique haploid gametes.
8.14 Mitosis and meiosis have important similarities and differences
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Figure 8.14
Prophase
Metaphase
Duplicatedchromosome(two sisterchromatids)
MITOSIS
Parent cell(before chromosome duplication)
Chromosomeduplication
Chromosomeduplication
Site ofcrossingover
2n 4
Chromosomesalign at themetaphase plate
Tetrads (homologouspairs) align at themetaphase plate
Tetrad formedby synapsis ofhomologouschromosomes
Metaphase I
Prophase I
MEIOSIS I
AnaphaseTelophase
Sister chromatidsseparate during
anaphase
2n 2n
Daughter cells of mitosis
No furtherchromosomalduplication;sisterchromatidsseparate duringanaphase II
n n n n
Daughter cells of meiosis II
Daughtercells of
meiosis I
Haploidn 2
Anaphase ITelophase I
Homologouschromosomesseparate duringanaphase I;sisterchromatidsremain together
MEIOSIS II
Figure 8.14_1
Prophase
Metaphase
MITOSIS
Parent cell(before chromosome duplication)
Chromosomeduplication
Chromosomeduplication
Site ofcrossingover
2n 4
Chromosomesalign at themetaphase plate
Tetrads (homologouspairs) align at themetaphase plate
Tetrad
Metaphase I
Prophase I
MEIOSIS I
Figure 8.14_2
Metaphase
MITOSIS
Chromosomesalign at themetaphase plate
AnaphaseTelophase
Sister chromatidsseparate during
anaphase
2n 2nDaughter cells of mitosis
Figure 8.14_3
Tetrads (homologouspairs) align at themetaphase plate
Metaphase I
No furtherchromosomalduplication;sisterchromatidsseparate duringanaphase II
n
Daughter cells of meiosis II
Daughtercells of
meiosis I
Haploidn 2
Anaphase ITelophase I
Homologouschromosomesseparate duringanaphase I;sisterchromatidsremain together
MEIOSIS II
MEIOSIS I
n n n
Genetic variation in gametes results from
– independent orientation at metaphase I and
– random fertilization.
8.15 Independent orientation of chromosomes in meiosis and random fertilization lead to varied offspring
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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.
8.15 Independent orientation of chromosomes in meiosis and random fertilization lead to varied offspring
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Random fertilization – The combination of each unique sperm with each unique egg increases genetic variability.
8.15 Independent orientation of chromosomes in meiosis and random fertilization lead to varied offspring
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Animation: Genetic Variation
Figure 8.15_s1
Possibility A
Two equally probablearrangements ofchromosomes at
metaphase I
Possibility B
Figure 8.15_s2
Possibility A
Two equally probablearrangements ofchromosomes at
metaphase I
Possibility B
Metaphase II
Figure 8.15_s3
Possibility A
Two equally probablearrangements ofchromosomes at
metaphase I
Possibility B
Metaphase II
Gametes
Combination 3 Combination 4Combination 2Combination 1
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.
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Figure 8.16
Coat-colorgenes
Eye-colorgenes
Brown Black
Meiosis
White Pink
Tetrad in parent cell(homologous pair of
duplicated chromosomes)
Chromosomes ofthe four gametes White coat (c);
pink eyes (e)
Brown coat (C);black eyes (E)
EC
ec
e
E
E
ec
c
C
C
20
Figure 8.16_2
Brown coat (C);black eyes (E)
Figure 8.16_3
White coat (c);pink eyes (e)
Figure 8.16_1
Coat-colorgenes
Eye-colorgenes
Brown Black
Meiosis
White Pink
Tetrad in parent cell(homologous pair of
duplicated chromosomes)
EC
ec
Chromosomes ofthe four gametes
e
E
E
ec
c
C
C
Figure 8.16Q
Sister chromatidsSister chromatids
Pair of homologouschromosomes
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.
8.17 Crossing over further increases genetic variability
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Animation: Crossing Over
Figure 8.17A
Chiasma
Tetrad
21
Figure 8.17A_1
Chiasma
Figure 8.17BTetrad
(pair of homologouschromosomes in synapsis)
Breakage of homologous chromatids
Joining of homologous chromatids
Chiasma
Separation of homologouschromosomes at anaphase I
Separation of chromatids atanaphase II andcompletion of meiosis
Parental type of chromosome
Recombinant chromosome
Recombinant chromosome
Parental type of chromosomeGametes of four genetic types
1
2
3
4
C
c e
E
C
c e
E
c e
C E
C e
e
C E
c
c E
C E
C e
c E
ec
Figure 8.17B_1
Tetrad(pair of homologouschromosomes in synapsis)
Breakage of homologous chromatids
Joining of homologous chromatids
1
2
C
c e
E
C
c e
E
C
c e
E
Chiasma
Figure 8.17B_2
Separation of homologouschromosomes at anaphase I
3
C E
C e
Chiasma
c
c
E
e
C E
c e
Figure 8.17B_3
Separation of chromatids atanaphase II andcompletion of meiosis
Parental type of chromosome
Recombinant chromosome
Recombinant chromosome
Parental type of chromosome
Gametes of four genetic types
C E
eC
4
Ec
c e
EC
eC
c E
c e
ALTERATIONS OF CHROMOSOME NUMBER
AND STRUCTURE
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22
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.
8.18 A karyotype is a photographic inventory of an individual’s chromosomes
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Figure 8.18_s1
Bloodculture
Packed redand whiteblood cells
Centrifuge
Fluid1
Figure 8.18_s2
Bloodculture
Packed redand whiteblood cells
Centrifuge
Fluid
Hypotonicsolution
2
1
Figure 8.18_s3
Bloodculture
Packed redand whiteblood cells
Centrifuge
Fluid
Hypotonicsolution Fixative
Whitebloodcells
Stain
3
2
1
Figure 8.18_s4
4
Figure 8.18_s5
Centromere
Sisterchromatids
Pair ofhomologouschromosomes
5
Sex chromosomes
23
Trisomy 21
– involves the inheritance of three copies of chromosome 21 and
– is the most common human chromosome abnormality.
8.19 CONNECTION: An extra copy of chromosome 21 causes Down syndrome
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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.
8.19 CONNECTION: An extra copy of chromosome 21 causes Down syndrome
© 2012 Pearson Education, Inc.
Figure 8.19A
Trisomy 21
Figure 8.19A_1
Trisomy 21
Figure 8.19A_2 Figure 8.19B
Age of mother
504540353025200
10
20
30
40
50
60
70
80
90
Infa
nts
wit
h D
ow
n s
ynd
rom
e(p
er 1
,000
bir
ths)
24
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.
8.20 Accidents during meiosis can alter chromosome number
© 2012 Pearson Education, Inc.
Figure 8.20A_s1
Nondisjunction
MEIOSIS I
Figure 8.20A_s2
Nondisjunction
MEIOSIS I
MEIOSIS II
Normalmeiosis II
Figure 8.20A_s3
Nondisjunction
MEIOSIS I
MEIOSIS II
Normalmeiosis II
Gametes
Number ofchromosomes
Abnormal gametes
n 1 n 1 n 1 n 1
Figure 8.20B_s1
Normalmeiosis I
MEIOSIS IFigure 8.20B_s2
Normalmeiosis I
MEIOSIS I
MEIOSIS II
Nondisjunction
25
Figure 8.20B_s3
Normalmeiosis I
MEIOSIS I
MEIOSIS II
Nondisjunction
Abnormal gametes Normal gametes
n 1 n 1 n n
Sex chromosome abnormalities tend to be less severe, perhaps because of
– the small size of the Y chromosome or
– X-chromosome inactivation.
8.21 CONNECTION: Abnormal numbers of sexchromosomes do not usually affect survival
© 2012 Pearson Education, Inc.
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.”
8.21 CONNECTION: Abnormal numbers of sexchromosomes do not usually affect survival
© 2012 Pearson Education, Inc.
Table 8.21
Errors in mitosis or meiosis may produce polyploid species, with more than two chromosome sets.
The formation of polyploid species is
– widely observed in many plant species but
– less frequently found in animals.
8.22 EVOLUTION CONNECTION: New species can arise from errors in cell division
© 2012 Pearson Education, Inc.
Figure 8.22
26
Chromosome breakage can lead to rearrangements that can produce
– genetic disorders or,
– if changes occur in somatic cells, cancer.
8.23 CONNECTION: Alterations of chromosome structure can cause birth defects and cancer
© 2012 Pearson Education, Inc.
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.
8.23 CONNECTION: Alterations of chromosome structure can cause birth defects and cancer
© 2012 Pearson Education, Inc.
Chronic myelogenous leukemia (CML)
– is one of the most common leukemias,
– affects cells that give rise to white blood cells (leukocytes), and
– results from part of chromosome 22 switching places with a small fragment from a tip of chromosome 9.
8.23 CONNECTION: Alterations of chromosome structure can cause birth defects and cancer
© 2012 Pearson Education, Inc.
Figure 8.23A
Deletion
Duplication
Inversion
Reciprocal translocation
Homologouschromosomes Nonhomologous
chromosomes
Figure 8.23A_1
Deletion
Duplication
Homologouschromosomes
Figure 8.23A_2
Inversion
Reciprocal translocation
Nonhomologouschromosomes
27
Figure 8.23B
Chromosome 9
Chromosome 22 Reciprocaltranslocation
“Philadelphia chromosome”
Activated cancer-causing gene
1. Compare the parent-offspring relationship in asexual and sexual reproduction.
2. Explain why cell division is essential for prokaryotic and eukaryotic life.
3. Explain how daughter prokaryotic chromosomes are separated from each other during binary fission.
4. Compare the structure of prokaryotic and eukaryotic chromosomes.
5. Describe the stages of the cell cycle.
You should now be able to
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6. List the phases of mitosis and describe the events characteristic of each phase.
7. Compare cytokinesis in animal and plant cells.
8. Explain how anchorage, cell density, and chemical growth factors control cell division.
9. Explain how cancerous cells are different from healthy cells.
10. Describe the functions of mitosis.
11. Explain how chromosomes are paired.
12. Distinguish between somatic cells and gametes and between diploid cells and haploid cells.
You should now be able to
© 2012 Pearson Education, Inc.
13. Explain why sexual reproduction requires meiosis.
14. List the phases of meiosis I and meiosis II and describe the events characteristic of each phase.
15. Compare mitosis and meiosis noting similarities and differences.
16. Explain how genetic variation is produced in sexually reproducing organisms.
17. Explain how and why karyotyping is performed.
18. Describe the causes and symptoms of Down syndrome.
You should now be able to
© 2012 Pearson Education, Inc.
19. Describe the consequences of abnormal numbers of sex chromosomes.
20. Define nondisjunction, explain how it can occur, and describe what can result.
21. Explain how new species form from errors in cell division.
22. Describe the main types of chromosomal changes. Explain why cancer is not usually inherited.
You should now be able to
© 2012 Pearson Education, Inc.
Figure 8.UN01
Geneticallyidenticaldaughtercells
SG1
G2
M
Mitosis(division ofthe nucleus)
Cytokinesis(division of thecytoplasm)
(DNA synthesis)
28
Figure 8.UN02
Haploid gametes (n 23)
Egg cell
Sperm cell
Fertilization
n
n
Meiosis
Human life cycle
2nMulticellulardiploid adults(2n 46)
Mitosis
Diploidzygote(2n 46)
Figure 8.UN03
Number of chromosomalduplications
Number of cell divisions
Number of daughter cellsproduced
Number of chromosomes inthe daughter cells
How the chromosomes lineup during metaphase
Genetic relationship of thedaughter cells to the parent cell
Functions performed in thehuman body
Mitosis Meiosis
Figure 8.UN04