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Introduction
Cancer cells
• start out as normal body cells,
• mutations,
• Lose cell cycle control
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Introduction
• In a healthy body, cell division allows for
• growth,
• the replacement of damaged cells, and
• development from an embryo into an adult.
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Figure 8.0-2
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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
• The ability of organisms to reproduce their own kind is a key
characteristic of life.
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8.1 Cell division plays many important roles in the lives of
organisms
• Cell division
• is reproduction at the cellular level,
• produces two identical “daughter” cells
• duplication of chromosomes,
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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
• offspring that are identical to the parent
• inheritance of all genes from one parent.
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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.
• Sexual reproduction
• offspring that are similar to the parents
• unique sets of genes from two parents.
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
Figure
8.1f production
• Gamete
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8.2 Prokaryotes reproduce by binary fission
• Prokaryotes (single-celled bacteria and archaea) reproduce by
binary fission (“dividing in half”).
• The chromosome of a prokaryote
• circular DNA molecule + proteins
Figure
8.2a-2
• smaller
than eukaryotes.
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Figure 8.2a-3
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Figure 8.2b
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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
• have more genes
• store most of their genes on multiple chromosomes within the
nucleus.
• Each eukaryotic species has a characteristic number of
chromosomes.
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chromosomes.
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8.3 The large, complex chromosomes of
eukaryotes duplicate with each cell division
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8.3 The large, complex chromosomes of
eukaryotes duplicate with each cell division
• Eukaryotic chromosomes are composed of chromatin
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• To prepare for division, the chromatin condenses
8.3 The large, complex chromosomes of
eukaryotes duplicate with each cell division
• To prepare for division, the chromatin condenses, thus becoming
visible in the microscope
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8.3 The large, complex chromosomes of
eukaryotes duplicate with each cell division
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8.3 The large, complex chromosomes of
eukaryotes duplicate with each cell division
• Before cell division, cells duplicate all of their chromosomes
sister chromatids.
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• The sister chromatids are joined together at a narrowed “waist”
called the centromere.
• When a cell divides, the sister chromatids
• separate from each other and are then called chromosomes, and
• sort into separate daughter cells.
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8.4 The cell cycle includes growing and division phases
• 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.
• Cytokinesis—division of cytoplasm
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8.4 The cell cycle includes growing and division phases
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8.5 Cell division is a continuum of dynamic changes
• Mitosis progresses through a series of stages:
• prophase,
• metaphase,
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• prophase,
• metaphase,
• anaphase, and
• telophase.
• organizing
Cytokinesisregions
often overlaps
telophase.
in the cytoplasm
of eukaryotic cells.
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Video: Animal Mitosis
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Video: Sea Urchin (time lapse)
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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.
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Figure 8.5-1
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8.5 Cell division is a continuum of dynamic
changes
• Prophase
• In the nucleus, chromosomes become more tightly coiled and
folded.
• In the cytoplasm, the mitotic spindle begins to form as
microtubules rapidly grow out from the centrosomes.
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Figure 8.5-1
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Figure 8.5-1
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8.5 Cell division is a continuum of dynamic changes
• Metaphase
• The mitotic spindle is fully formed.
• Chromosomes align at the cell equator.
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8.5 Cell division is a continuum of dynamic changes
• Prometaphase
• The nuclear envelope breaks down
• Microtubules extend from the centrosomes
• Some spindle microtubules attach to the kinetochores.
• Other microtubules meet those from the opposite poles.
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• The mitotic spindle is fully formed.
• Chromosomes align at the cell equator.
• Kinetochores of sister chromatids are facing the opposite poles of
the spindle.
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Figure 8.5-6
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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
as motor proteins move the chromosomes along the spindle
microtubules and kinetochore microtubules shorten.
• Spindle microtubules not attached to chromosomes lengthen,
moving the poles farther apart.
• At the end of anaphase, the two ends of the cell have equal
collections of chromosomes.
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Figure 8.5-6
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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.
• The mitotic spindle disappears.
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Figure 8.5-6
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8.5 Cell division is a continuum of dynamic changes
• During cytokinesis, the cytoplasm is divided into separate cells.
• Cytokinesis usually occurs simultaneously with telophase.
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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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cells.
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Figure
8.6a-0
3. each
cell now possesses a plasma membrane and cell wall.
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8.6 Cytokinesis differs for plant and animal cells
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Animation: Cytokinesis
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8.7 Anchorage, cell density, and chemical growth factors affect
cell division
• The cells within an organism’s body divide and develop at different
rates.
• Cell division is controlled by
• anchorage dependence, the need for cells to be in contact with a
solid surface to divide,
• density-dependent inhibition, in which crowded cells stop
dividing,
• the presence of essential nutrients, and
• growth factors, proteins that stimulate division.
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Figure 8.7a
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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
in• signal
biologyantoday.
event to proceed.
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Figure 8.7b
8.8 Growth factors signal the cell cycle control system
Figure 8.8b
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Figure 8.8b
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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.
• Cancer cells escape controls on the cell cycle.
• Cancer cells divide excessively and invade other tissues of the
body.
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• Cancer cells divide excessively and invade other tissues of the
body.
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8.9 CONNECTION: Growing out of control, cancer cells produce
malignant tumors
• A tumor is a mass of abnormally growing cells within otherwise
normal tissue.
• Benign tumors remain at the original site but may disrupt certain
organs if they grow in size.
• Malignant tumors can spread to other locations in a process
called metastasis.
• An individual with a malignant tumor is said to have cancer.
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Figure 8.9
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Concept Check
• What role(s) does cell division play in your own body?
a)Production of gametes
b)Growth
c)Repair and replacement of dying cells
d)Early development of the embryo following fertilization
e)All of the above
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Answer
• What role(s) does cell division play in your own body?
a)Production of gametes
b)Growth
c)Repair and replacement of dying cells
d)Early development of the embryo following fertilization
e)All of the above
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Concept Check
• Use the following choices to complete the table at the left:
a)Mitosis
b)Meiosis
c)Both
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c)Both
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Answer
• Use the following choices to complete the table at the left:
a)Mitosis
b)Meiosis
c)Both
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Answer
• Use the following choices to complete the table at the left:
a)Mitosis
b)Meiosis
c)Both
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Answer
• Use the following choices to complete the table at the left:
a)Mitosis
b)Meiosis
c)Both
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Answer
• Use the following choices to complete the table at the left:
a)Mitosis
b)Meiosis
c)Both
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Answer
• Use the following choices to complete the table at the left:
a)Mitosis
b)Meiosis
c)Both
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Answer
• Use the following choices to complete the table at the left:
a)Mitosis
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a)Mitosis
b)Meiosis
c)Both
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Concept Check
• Which of the following contribute to variation in offspring in sexually
reproducing organisms?
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a)independent orientation of chromosomes during meiosis
b)crossing over during tetrad formation
c)sexual reproduction
d)all of the above
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Answer
• Which of the following contribute to variation in offspring in sexually
reproducing organisms?
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a)independent orientation of chromosomes during meiosis
b)crossing over during tetrad formation
c)sexual reproduction
d)all of the above
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Biology and Society
• One of the first human cell lines to survive indefinitely was that
derived from a cancer patient who died in 1951. Known as the
HeLa line for Henrietta Lacks, the cell line continues today in
laboratories throughout the world and is even available for high
school classrooms to study karyotyping. In 1951, people didn’t fully
realize the potential applications of unique cells or DNA. Do you
think that a patient should retain all rights to their cells or DNA
Table
8.10
during
medical procedures?
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MEIOSIS AND CROSSING OVER
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8.11 Chromosomes are matched in homologous pairs
• In humans, somatic cells have 46 chromosomes forming 23 pairs of
homologous chromosomes.
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8.11 Chromosomes are matched in homologous pairs
• Homologous chromosomes are matched in
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8.11 Chromosomes are matched in homologous pairs
• Homologous chromosomes are matched in
• length,
• centromere position, and
• staining pattern.
• A locus (plural, loci) is the position of a gene.
8.11 Chromosomes are matched in homologous pairs
• 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.
Figure
8.11
somatic
cells contain pairs of homologous chromosomes.
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8.12
haveform.
a single set of chromosomes
cellsGametes
into the adult
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8.12 Gametes have a single set of chromosomes
Meiosis
= Gametes
the
ovaries
anddivision.
testes.
• mitosis
is followedinby
only
one cell
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8.13 Meiosis reduces the chromosome number from diploid to
haploid
• Interphase: Like mitosis, meiosis is preceded by an interphase,
during
which
the chromosomes
duplicate.
• Usually,
cytokinesis
occurs along
with telophase.
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Figure
8.13-5chromosomes move toward opposite poles.
• Individual
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Figure 8.13-4
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Figure 8.13-7
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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.
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8.14 VISUALIZING THE CONCEPT: 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 produces two genetically identical diploid somatic
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• However, the end products differ.
• Mitosis produces two genetically identical diploid somatic
daughter cells.
• Meiosis produces four genetically unique haploid gametes.
Figure 8.14-1
Figure 8.14-2
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Figure 8.14-3
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Figure 8.14-4
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Figure 8.14-6
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Animation: Genetic Variation
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Figure 8.15-1
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Figure 8.15-2
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Figure
8.15-3
version
of the gene.
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8.16 Homologous chromosomes may carry different versions of
genes
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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
nonsister chromatids of 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.
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Figure 8.14-5
8.15 Independent orientation of chromosomes in meiosis and
random fertilization lead to varied offspring
• Genetic variation in gametes results from
• independent orientation at metaphase I and
• random
sperm
withfertilization.
each unique egg increases genetic variability.
between maternal and paternal (nonsister) chromatids.
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Animation: Crossing Over
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Figure 8.17a-0
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Figure 8.17b-0
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ALTERATIONS OF CHROMOSOME NUMBER AND STRUCTURE
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8.18 Accidents during meiosis can alter chromosome number
• Nondisjunction is the failure of chromosomes or chromatids to
separate normally during meiosis.
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8.18 Accidents during meiosis can alter chromosome number
• Nondisjunction is the failure of chromosomes or chromatids to
separate normally during meiosis.
• meiosis I (homologous pairs)
• meiosis II (sister chromatids)
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Figure 8.18-1-1
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Figure 8.18-1-2
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Figure 8.18-1-3
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Figure 8.18-2-2
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Figure 8.18-2-3
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8.19 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
• allow for the observation of
• homologous chromosome pairs,
• chromosome number, and
• chromosome structure.
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Figure 8.19-3
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Figure 8.19-3
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8.19 A karyotype is a photographic inventory of an individual’s
chromosomes
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8.19 A karyotype is a photographic inventory of an individual’s
chromosomes
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8.19 A karyotype is a photographic inventory of an individual’s
chromosomes
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8.19 A karyotype is a photographic inventory of an individual’s
chromosomes
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8.19 A karyotype is a photographic inventory of an individual’s
chromosomes
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8.20 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.
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8.20 CONNECTION: An extra copy of chromosome 21 causes
Down syndrome
• A person with trisomy 21 has a condition called Down syndrome,
which produces a characteristic set of symptoms, including
• characteristic facial features,
• short stature,
• heart defects,
• susceptibility to respiratory infections, leukemia, and Alzheimer’s
disease, and
• varying degrees of developmental disabilities.
• The incidence increases with the age of the mother.
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Figure 8.20a-0
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8.21 CONNECTION: Abnormal numbers of sex chromosomes
do not usually affect survival
• Sex chromosome abnormalities seem to upset the genetic balance
less than an unusual number of autosomes. This may be because
of
• the small size of the Y chromosome or
• X chromosome inactivation.
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• the small size of the Y chromosome or
• X chromosome inactivation.
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.”
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8.21 Abnormal numbers of sex chromosomes do not usually
affect survival
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8.23 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.
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8.23 Alterations of chromosome can lead to four types of
changes in chromosome structure
1. A deletion is the loss of a chromosome segment.
2. A duplication is the repeat of a chromosome segment.
3. An inversion is the reversal of a chromosome segment.
4. A translocation is the attachment of a segment to a
nonhomologous chromosome. A translocation may be
reciprocal.
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8.23 CONNECTION: Alterations of chromosome structure can
cause birth defects and cancer
• Inversions are less likely than deletions or duplications to produce
harmful effects, because in inversions all genes are still present in
their normal number.
• Many deletions cause serious physical or mental problems.
• to
Translocations
or may
notusually
be harmful.
somatic cells,may
cancer
is not
inherited.
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Figure 8.23a-0
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Figure 8.23b
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You should now be able to
1. Compare the parent-offspring relationship in asexual and sexual
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You should now be able to
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.
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You should now be able to
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.
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You should now be able to
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.
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You should now be able to
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
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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.
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Figure 8.0-0
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Figure 8.UN01
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Figure 8.UN02
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Figure 8.UN03
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Figure 8.UN04