Download Unit 3 - Transmission and Transmission and Molecular Genetics

Unit 3 - Transmission and
Molecular Genetics
Unit 3 Transmission and
Molecular Genetics
Genetics is the scientific study of
inheritance and the hereditary material:
 Transmission genetics deals with how
the genetic material is passed on from
one cell to another during the cell
cycle, and from one organism to
another during the life cycle.
 Molecular
genetics deals with the
structure and function of the genetic
material at the molecular level.
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Module 3A – Cell Reproduction
Unit 3 - Transmission and
Molecular Genetics
 In
this module, we will examine the
cell cycle
cycle,, the series of changes that a
cell goes through from one generation
to the next
next.
 We will pay particular attention to how
the genetic material is passed on from
parent cell to daughter cells during the
cell cycle.
3A. How Cells Divide
3B. Meiosis and Sexual Life Cycles
3C. Patterns of Inheritance
3D. Chromosomes and Inheritance
3E. DNA Structure and Replication
3F. Protein Synthesis
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Objective # 1
Objective 1
 An
Compare the amount and
organization of genetic material in
prokaryotic cells with the amount
and organization of genetic
material in eukaryotic cells.
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average eukaryotic cell has about
1,000 times more DNA then an
average prokaryotic cell.
 The DNA in a eukaryotic cell is
organized into several linear
chromosomes, whose organization is
much more complex than the single,
circular DNA molecule found in a
prokaryotic cell:
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1
Objective 1
DNA
Prokaryotes
structure single, naked,
circular DNA
molecule; attached
to 1 point on the
inner surface of
plasma membrane
location in an area of the
cytoplasm called
the nucleoid
Objective 1
Eukaryotes
many linear
chromosomes,
each made of 1
DNA molecule
joined with
protein
inside a
membrane-membrane
bound nucleus
 If
the DNA of either a prokaryotic or
eukaryotic cell were completely
stretched out, it would thousands of
times longer than the cell itself.
 Therefore, the DNA must be folded
and coiled so it will fit into the cell.
 On the next slide, you can see how this
is done in a prokaryotic cell:
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Objective # 2
Describe the process of cell
prokaryotic
y
cells.
division in p
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Objective 2
Prokaryotes use a type of cell division
called binary fission:
fission:
1) First, the single, circular DNA
molecule replicates, producing two
id i l copies
identical
i off the
h original.
i i l
Replication begins at a specific site
called the origin of replication and
proceeds bidirectionally around the
circle to a specific site of termination:
termination:
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Objective 2
Objective 2
2) As the DNA replicates, growth of the
cell results in elongation. After
replication is complete, the DNA
molecules are actively partitioned to
¼ and ¾ of the cell length. During
this process, specific DNA sequences
near the origin of replication are
attached to the plasma membrane.
3) Finally, the cytoplasm is divided in
half by the growth of a new
membrane and septum in the middle
of the cell. This produces 2 daughter
cells which are genetically identical
(unless a mutation occurred) to each
other and to the original cell:
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Bacterial cell
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Binary Fission – part 1
Binary Fission – part 2
1. Prior to cell division, the bacterial DNA
molecule replicates. The replication of the
Bacterial DNA
Origin of double-stranded, circular DNA molecule that
replication constitutes the genome of a bacterium
begins at a specific site, called the origin of
replication (green area).
2. The replication enzymes move out in both
directions from that site and make copies
of each strand in the DNA duplex.
p
The
enzymes continue until they meet at
another specific site, the terminus of
replication (red area).
Septum
4. Septation begins, in which new cell membrane and cell wall
material begins to grow and form a septum at approximately the
midpoint of the cell. A protein molecule called FtsZ (orange dots)
f ilit t thi
facilitates
this process.
3. As the DNA is replicated, the cell
elongates, and the DNA is partitioned in
the cell such that the origins are at the ¼
and ¾ positions in the cell and the termini
are oriented toward the middle of the cell.
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When the septum is complete, the cell pinches
5. in two, and two daughter cells are formed,
each containing a bacterial DNA molecule.
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Objective # 3
Describe the structure of both
duplicated and unduplicated
eukaryotic chromosomes; and
distinguish between
chromosome, chromatid,
centromere, and chromatin.
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3
Objective 3
Objective 3
 Eukaryotic
chromosomes are made
of chromatin,
chromatin, a complex of DNA
and protein.
Each unduplicated chromosome
contains one DNA molecule, which
may be several inches long.
How can such long molecules fit inside
a microscopic nucleus?
Every 200 nucleotide pairs, the DNA
wraps twice around a group of 8 histone
proteins to form a nucleosome
nucleosome..
Higher order coiling and supercoiling
also help condense and package the
chromatin inside the nucleus:
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Objective 3
Levels of DNA Coiling in a Chromosome
Rosettes of
Chromatin
Chromosome Chromatin Loops
Loop
Scaffold
protein
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Permission required for reproduction or display.
The degree of coiling can vary in
Solenoid
different regions of the chromatin:
Heterochromatin refers to highly
coiled regions where genes aren
aren’tt
expressed.
Euchromatin refers to loosely
coiled regions where genes can be
expressed.
Chromatin loop
DNA Double Helix
Nucleosome
Histone core
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DNA
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Objective 3
 For
much of the cell cycle, most
chromatin is loosely coiled.
 During this time, only the
heterochromatin is visible,
visible as dense
granules inside the nucleus.
 There is also a dense area of RNA
production called the nucleolus:
Nucleus
Chromatin
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Objective 3
Fully Condensed Human Chromosomes
 Prior
to cell division each
chromosome duplicates itself.
 All the duplicated chromosomes
then condense into short rodrod-like
structures that can be seen and
counted under the microscope:
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Objective 3
 Because
of duplication, each
condensed chromosome consists of 2
identical chromatids held together by a
complex of proteins called cohesins.
cohesins.
 Each duplicated chromosome contains
2 identical DNA molecules (unless a
mistake occurred during replication),
one in each chromatid.
Objective 3
Two Unduplicated
Homologous chromosomes
 The
centromere is a constricted region
of the chromosome where the 2
chromatids remain connected from the
middle of prophase to the start of
anaphase
anaphase.
 It contains repeated DNA sequences
that bind specific proteins. These
proteins make up a diskdisk-like structure
called the kinetochore.
kinetochore.
Two Duplicated
Homologous chromosomes
Kinetochore
Replication
Cohesin
proteins
Centromere
Kinetochores
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Sister chromatids
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Non- sister chromatids
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Objective 3
Metaphase Chromosome
 Kinetochores
serve as points of
attachment for a network of
microtubules that move the
chromosomes during cell division:
Cohesin
proteins
Chromatid
Centromere
i off
region
chromosome
Kinetochore
Kinetochore
microtubules
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Objective # 4
Objective 4
 The
particular array of chromosomes in
a eukaryotic cell is called its karyotype.
karyotype.
 To examine a karyotype, the
chromosomes are p
photographed
g p
when
they are highly condensed, then photos
of the individual chromosomes are cut
out and arranged in order of decreasing
size:
Explain what karyotypes are
and how theyy are useful.
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Objective 4
 Karyotypes
are used to study the
number and structure of the
chromosomes present in a cell.
 They
Th can also
l be
b used
d to ddetect
chromosomal abnormalities that may
be associated with specific genetic
traits or defects.
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Objective # 5
Objective 5
 In
eukaryotes, every species requires a
specific number of chromosomes to
code for all the polypeptides produced
by the organism. These chromosomes
make up 1 complete set.
 Each chromosome in a set controls
the production of a different group of
polypeptides.
Distinguish between a haploid
cell and a diploid cell.
Distinguish between identical
chromosomes, homologous
chromosomes, and nonnonhomologous chromosomes.
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Objective 5
Objective 5
 Cells
that contain 1 complete set of
chromosomes are called haploid.
haploid.
 n or N = number of chromosomes in
a haploid
p
cell.
 Cells that contain 2 complete sets of
chromosomes are called diploid.
diploid.
 2n or 2N = number of chromosomes
in a diploid cell.
 For
example, 23 different
chromosomes are needed to code for
all the polypeptides produced by
humans.
 Therefore,
in humans:
N=23
2N = 46
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Objective 5
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Objective 5
 We
will use different shapes to
represent the different chromosomes
that make up a set, and different colors
to represent different sets of
chromosomes.
Unduplicated Chromosomes
Haploid Cell, N = 3 Diploid Cell, 2N = 6
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Objective 5
Objective 5
Duplicated Chromosomes
 In
Haploid Cell, N = 3 Diploid Cell, 2N = 6
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
Objective 5
However, homologous chromosomes are
not identical because they may code for
different forms of each trait. Therefore we
will represent them using 2 different colors:
Red eyes
Short wings
Tan body
White eyes
Long wings
Tan body
a diploid cell, the chromosomes
occur in pairs. The 2 members of each
pair are called homologous
chromosomes or homologues.
homologues.
 Under the microscope, homologous
chromosomes look identical.
 In addition, because they code for the
same polypeptides, they control the
same traits.
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Objective 5
 Identical
chromosomes:
Look the same
Control the same traits
Code for the same form of each trait
Common origin – they have both
descended from the same original
chromosome. (When the 2 halves of a
duplicated chromosome separate, we
get 2 identical chromosomes.)
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46
Objective 5
 Homologous
Objective 5
chromosomes:
Non-homologous
Chromosomes
 Look
the same
 Control the same traits
 May
y code for different forms of each trait
 Independent origin - each one was inherited
from a different parent
Homologous
Chromosomes
 Non
Non--homologous chromosomes:
 Look
different
 Control different traits
Diploid Cell, 2N = 6
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Objective # 6
Objective 6
 Gene
– a section of a DNA molecule
that contains the code for making one
polypeptide.
 Gene locus –the location of a g
gene
along the length of a chromosome
 Alleles – genes that can occupy the
same gene locus (on different
chromosomes)
Define and be able to use the
following terms correctly: gene,
gene locus,
l
and
d allele.
ll l
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Objective 6
Objective # 7
Homologous Chromosomes
Red eyes
Short wings
Tan body
White eyes
Long wings
Tan body
Identify the stages of the
eukaryotic
y
cell cycle,
y , and
describe the events of each
stage.
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Objective 7
 The
cell cycle refers to the sequence of
events that occur as a cell grows and
divides. It is divided into 2 main stages:
 Interphase
p
– chromosomes are not
visible. Involves cell growth and
duplication of the genetic material.
 Cell division – includes division of the
duplicated chromosomes ((mitosis
mitosis)) and
division of the cytoplasm (cytokinesis
(cytokinesis).
). 53
Objective 7
 Interphase
is subdivided into 3 stages:
 G1 is the primary growth phase of the
cell cycle
 S is
s when
w e the
t e cell
ce synthesizes
sy t es es a copy of
o
its chromosomes (DNA duplication).
 G2 is the second growth phase, during
which preparations are made for cell
division.
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9
Stages of the Cell Cycle
Objective 7
M
 Mitosis
is subdivided into 5 stages:
Prophase
Prometaphase
Metaphase
Anaphase
Telophase
Metaphase
Prometaphase
Anaphase
Prophase
Telophase
C
G2
G1
S Interphase
G2
M- Mitosis
C- Cytokinesis
G1
S
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Objective # 8
List, describe, diagram, and
identifyy the stages
g of mitosis.
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Objective 8
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Some diploid cells divide by mitosis:
 Mitosis:
DNA duplication during
interphase
 some
haploid and some diploid cells
divide by mitosis.
 eac
each new
ew cell
ce receives
ece ves one
o e copy of
o
every chromosome that was present in
the original cell.
 produces 2 new cells that are both
genetically identical to the original cell.
Diploid Cell
Mitosis
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Some haploid cells can also divide by mitosis:
Objective 8
Stages of Mitosis in Diploid Cell, 2N = 6
 Prophase:
 duplicated chromosomes condense and
becomee vvisible
beco
sbe
 cytoskeleton is disassembled; mitotic
spindle begins to form
 Golgi and ER are dispersed
 nuclear envelope disintegrates
DNA duplication during
interphase
Haploid Cell
Mitosis
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Objective 8
Prophase
 Prometaphase
Prometaphase::
 chromosomes
attach to microtubules at
the kinetochores
 each chromosome is oriented so that the
kinetochores of sister chromatids are
attached to microtubules from opposite
poles
 chromosomes move toward equator of
cell
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Objective 8
Prometaphase
 Metaphase:
 chromosomes
are aligned, in single
file, along metaphase plate at the
equator of cell
 chromosomes are attached to
opposite poles and are under
tension
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11
Objective 8
Metaphase
 Anaphase:
 centromeres
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Anaphase
split so that each
duplicated chromosome becomes 2
identical, unduplicated
p
chromosomes
 kinetochore microtubules shorten,
pulling identical chromosomes to
opposite poles
 polar microtubules elongate preparing
cell for cytokinesis
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Objective 8
 Telophase:
Kinetochore
Microtubule
 chromosomes
Polar Microtubule
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cluster at opposite poles
of the cell and decondense
 kinetochores disappear
 polar microtubules continue to
elongate, preparing cell for cytokinesis
 nuclear envelope reforms
 Golgi complex, ER and cytoskeleton
reform
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Stages of Mitosis in Haploid Cell, N = 3
Telophase
Prophase
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Prometaphase
Metaphase
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Anaphase
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Telophase
Kinetochore
Microtubule
Polar Microtubule
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Objective # 9
Describe the process of
y
and distinguish
g
cytokinesis
between mitosis and
cytokinesis.
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Objective 9
Objective 9
 Cytokinesis
refers to division of the
cytoplasm during cell division, while
mitosis refers to division of the genetic
material (chromosomes).
 In
animal cells and other eukaryotic
cells that lack a cell wall, cytokinesis is
achieved by means of a constricting
belt of actin filaments.
 As the filaments slide past each other,
they create a cleavage furrow which
deepens and eventually pinches the cell
in half:
 Although
cytokinesis generally follows
mitosis, this isn’t always the case.
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Objective 9
 Plant
cells possess a cell wall which is
too rigid to be squeezed in half by
actin filaments.
 Instead, a new cell membrane, called a
cell plate
plate,, is assembled in the middle of
the cell. As this expands outward, it
effectively divides the cell in two.
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Objective # 10
Explain how the eukaryotic
y is controlled.
cell cycle
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Objective 10
Objective 10
 The
eukaryotic cell cycle is
controlled by a complex interaction
of internal and external regulatory
molecules.
 The
 Some
of these molecules act to
stimulate cell division while others
act to inhibit it.
87
Objective 10
level of these regulatory molecules
affects 3 principal checkpoints at which
the cycle can be delayed or halted.
 The cell uses these checkpoints
p
to both
assess its internal state and evaluate
external signals.
 The cell proceeds past each checkpoint
only if internal and external conditions
are favorable.
G2 / M checkpoint
 the
G1/S checkpoint assess cell growth.
This is the primary point at which the cell
decides whether or not to divide.
 the G2/M checkpoint ensures DNA
integrity At this point the cell assesses the
integrity.
accuracy of DNA replication.
 the Spindle checkpoint ensures that all the
chromosomes are attached to spindle
fibers, with bipolar orientation, in
preparation for anaphase.
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Spindle checkpoint
M
C
G2
Cell Cycle
Control
S
89
G1
G1 / S checkpoint
(Start or Restriction Point)
90
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Objective 10
Activation of Cdk
 To
pass each checkpoint, enzymes called
Cyclin--dependent kinases (Cdks
Cyclin
Cdks)) must be
activated.
 Full activation of Cdks requires
q
bindingg
with specific regulatory proteins called
cyclins, along with the appropriate
pattern of phosphorylation:
P
Phosporylation of the red site
inactivates Cdk
Cyclin
Cyclin-dependent
Kinase (Cdk)
Phosporylation of the
green site activates
Cdk
P
91
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Objective 10
Objective 10
 The
cyclin
cyclin--Cdk complex, is also called
MPF or mitosis promoting factor.
 MPF activates numerous proteins
needed for the next stage of the cell
cycle
l by
b phosphorylating
h h l i them.
h
 When the level of MPF is high
enough, the cell passes through the
checkpoint and enter the next stage of
the cell cycle.
 Different
cyclins must bind with Cdk
to pass each checkpoint.
 The cyclins needed to pass a specific
checkpoint
p
are synthesized duringg the
stage preceding that checkpoint, and
are quickly degraded during the stage
following that checkpoint:
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Objective 10
 In
multicellular organisms, passage
through cell cycle check points is
stimulated by external signal molecules
factors.
called ggrowth factors.
 Over
50 different growth factors have
been identified, and each one binds to a
different cell surface receptor.
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Objective 10
 When
a growth factor binds to its
surface receptor, this triggers an
intracellular signaling cascade that
activates regulatory proteins inside the
nucleus.
 The activated nuclear regulatory
proteins stimulate DNA to produce
proteins (e.g. Cdk or cyclins) needed to
pass through cell cycle checkpoints:
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Objective 10
Objective 10
 When
 While
growth factors act to stimulate
cell division, other regulatory molecules
mayy inhibit it.
 An example is a protein named p53:
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normal p53 detects damaged
DNA, it stops cell division by
preventing cyclins from joining to
Cdk.
 Abnormal p53 fails to stop division in
cells with damaged DNA. If genetic
damage accumulates as the cell
continues to divide, the cell can turn
cancerous.
100
Cell Division and Abnormal p53
Cell Division and Normal p53
p53 allows cells
with repaired
DNA to divide.
Abnormal
p53 protein
p53
protein
DNA repair enzyme
Cancer
cell
p53
protein
Step 1
DNA damage is
caused by heat,
radiation, or
chemicals.
Step 2
Step 1
Step 3
Cell division stops,
and p53 triggers
enzymes to repair
damaged region.
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p53 triggers the
destruction of cells
damaged beyond
repair.
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DNA damage is
caused by heat,
radiation, or
chemicals.
Step 2
The p53 protein fails to
stop cell division and
repair DNA. Cell
divides without repair
to damaged DNA.
Step 3
Damaged cells continue to
divide. If other damage
accumulates, the cell can
turn cancerous.
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Objective # 11
Objective 11
 Cancer
is the uncontrolled growth and
division of cells.
 Most cancers result from mutations in
one of two types
p of ggrowthgrowth-regulating
g
g
genes:
 proto
proto--oncogenes
 tumor
tumor--suppressor genes
Explain what cancer is, and
describe how cancer can
result when control of the
eukaryotic cell cycle breaks
down.
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Objective 11
Objective 11
 Proto
Proto--oncogenes
code for proteins
involved in stimulating cell division
(e.g. growth factors, growth factor
receptors, cyclins)
 Mutated proto
proto--oncogenes that
stimulate a cell to divide when it
shouldn’t are called oncogenes
(cancer--causing genes).
(cancer
 Tumor
Tumor--suppressor
genes code for
proteins involved in inhibiting cell
division (e.g. p53).
 Mutated
tumortumor-suppressor genes that
do not inhibit cell division when they
should can also cause cancer.
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