Paclitaxel-resistant human ovarian cancer cells undergo c-Jun NH2
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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.
Chapter 8 The Cellular Basis of Reproduction and Inheritance
© 2012 Pearson Education, Inc.
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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
© 2012 Pearson Education, Inc.
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CELL DIVISION AND REPRODUCTION
© 2012 Pearson Education, Inc.
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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.
© 2012 Pearson Education, Inc.
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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
© 2012 Pearson Education, Inc.
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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.
© 2012 Pearson Education, Inc.
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Figure 8.1A Yeast cell asexually reproducing
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Figure 8.1B Sea star reproducing asexually
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Figure 8.1C African violet leaf cutting reproducing asexually
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Figure 8.1D Sexual reproduction produces offspring that are similar to the parents, but show variations in traits
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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
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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
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Figure 8.2A
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
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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 A plant cell (from an African blood lily) just before cell division
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Figure 8.3B
Sisterchromatids
Chromosomes
Centromere
Chromosomeduplication
Sisterchromatids
Chromosomedistribution
to thedaughter
cells
DNA molecules
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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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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
CytokinesisM
itosi
s
I N T E R P H A S E
PHASE
TT
MI
OIC
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Mitosis progresses through a series of stages:
– prophase,
– metaphase,
– anaphase, and
– telophase.
Cytokinesis occurs at end of 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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Figure 8.5
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 in G phases,
– two centrosomes containing ____ form,
– chromatin duplicates in the nucleus during the S phase
8.5 Cell division is a continuum of dynamic changes
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Prophase
– In the cytoplasm microtubules begin to emerge from centrosomes, forming the ____.
– In the nucleus
– chromatin coils and becomes compact to form ____.
8.5 Cell division is a continuum of dynamic changes
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Metaphase
– Spindle microtubules reach chromosomes, where they
– attach on the centromeres and move ____ to the center of the cell
– The nuclear envelope disappears.
– ____ align at the cell equator.
8.5 Cell division is a continuum of dynamic changes
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Figure 8.5
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
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Figure 8.5
MITOSIS
AnaphaseMetaphase Telophase and Cytokinesis
Metaphaseplate
Cleavagefurrow
Nuclearenvelopeforming
Daughterchromosomes
Mitoticspindle
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Anaphase – Sister chromatids separate at the centromeres.
– Daughter chromosomes are moved to opposite poles of the cell as ____ shortens.
8.5 Cell division is a continuum of dynamic changes
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Figure 8.5
Anaphase
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Telophase– The cell continues to elongate.
– The nuclear envelope forms around chromosomes at each pole, establishing daughter nuclei.
– Chromosomes uncoil to form ____.
– The spindle breaks down.
8.5 Cell division is a continuum of dynamic changes
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Figure 8.5
Telophase and Cytokinesis
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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 ____ forms and deepens to separate the contents into two cells.
8.6 Cytokinesis differs for plant and animal cells
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Figure 8.6A
CytokinesisCleavage
furrow
Daughtercells
Cleavagefurrow
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In plant cells, cytokinesis occurs as1. a cell plate forms in the middle
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 ____.
8.6 Cytokinesis differs for plant and animal cells
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Figure 8.6B
Cytokinesis
Cell wallof theparent cell
Daughternucleus
Cell wall
Plasmamembrane
Vesiclescontainingcell wallmaterial
Cell plateforming
Newcell wall
Cell plate Daughtercells
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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
– Undergo mitosis rapidly
– 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
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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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Laboratory--Onion growing by mitosis
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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
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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)
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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
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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
– Each pair, with four chromatids, is called a tetrad.
– Tetrads exchange genetic material by crossing over.
8.13 Meiosis reduces the chromosome number from diploid to haploid
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Figure 8.13
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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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
Cleavagefurrow
Telophase I and Cytokinesis Prophase II Metaphase II Anaphase II
MEIOSIS II: Sister chromatids separate
Sister chromatidsseparate
Haploid daughtercells forming
Telophase IIand Cytokinesis
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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
Chromosomesare duplicated
Chromosomesare duplicatedParent cell
2n = 4
Homologouschromosomesremain separate
Chromosomesline up at themetaphase plate
Sisterchromatids
are separated2n
MITOSIS
Prophase
Metaphase
AnaphaseTelophase
2n
Prophase I
Metaphase I
Anaphase ITelophase I
MEIOSIS I
MEIOSIS II
Homologouschromosomespair up
Crossing over
Pairs ofhomologouschromosomesline up at the metaphase plate
Homologouschromosomesare separated
Sister chromatidsremain attached
Sisterchromatidsare separated
n = 2 n = 2
n n n n
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Figure 8.14
MITOSIS MEIOSIS I
MEIOSIS II
One division of the nucleus and cytoplasm
Result: Two genetically identical diploid cells
Used for: Growth, tissue repair, asexual reproduction
Two divisions of the nucleus and cytoplasm
Result: Four genetically unique haploid cells
Used for: Sexual reproduction
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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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Figure 8.15
Possibility A
Two equally probablearrangements ofchromosomes at
metaphase I
Possibility B
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Figure 8.15
Possibility A
Two equally probablearrangements ofchromosomes at
metaphase I
Possibility B
Metaphase II
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Figure 8.15
Possibility A
Two equally probablearrangements ofchromosomes at
metaphase I
Possibility B
Metaphase II
Gametes
Combination 3 Combination 4Combination 2Combination 1
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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 ____ 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
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Genetic recombination is the production of new combinations of genes due to crossing over.
Crossing over is an exchange of corresponding segments between chromatids on homologous chromosomes.
– Corresponding amounts of genetic material are exchanged between maternal and paternal chromatids.
8.17 Crossing over further increases genetic variability
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Figure 8.17A-BTetrad
(pair of homologouschromosomes in synapsis)
Breakage of homologous chromatids
Joining of homologous chromatids
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
Chiasma
Sisterchromatids
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ALTERATIONS OF CHROMOSOME NUMBER
AND STRUCTURE
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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 8.19
4
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Figure 8.19
Centromere
Sisterchromatids
Pair ofhomologouschromosomes
5
Sex chromosomes
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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
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Figure 8.20A
A person with Down syndrome
Trisomy 21
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Figure 8.20B
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)
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Figure from Laboratory