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Chapter 7
DNA Detective
Complex Patterns of Inheritance and DNA Fingerprinting
PowerPoint lecture prepared by
Steve McCommas
Southern Illinois State University
Copyright © 2010 Pearson Education, Inc.
DNA Detective
 1918: the Romanovs and four servants
were murdered by Communists
 1991: shallow grave containing bones of at
least nine people dug up
 Were any of these the Romanovs? If so,
which ones?
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7.1 Forensic Science
 Bones seemed to belong to six adults and
three children
 Sexing was inconclusive, due to
decomposition of pelvises
 Skeletons might be the Romanovs.
 Could resemblance among relatives be
useful?
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7.2 Dihybrid Crosses
 Dihybrid crosses: crosses involving two genes
simultaneously
 Mendel’s peas: seed color and seed shape are
on different chromosomes.
 Y = yellow seed color; y = green seed color; R =
smooth seeds; r = wrinkled seeds
 Cross between two double heterozygote parents:
YyRr x YyRr
 The following Punnett square shows expected
numbers of genotypes and phenotypes:
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7.2 Dihybrid Crosses - Punnett Square
RrYy
RrYy
Possible types of ovules
Possible types
of pollen
Phenotype
Genotype
9
Round, yellow
RRYY, RrYY, RRYy, RrYy
3
Round, green
Rryy, Rryy
3
Wrinkled, yellow rrYY, rrYy
1
Wrinkled, green rryy
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RRYY
round, yellow
RRYy
round, yellow
RrYY
round, yellow
RrYy
round, yellow
RRYy
round, yellow
Rryy
round, green
RrYy
round, yellow
Rryy
round, green
RrYY
round, yellow
RrYy
round, yellow
rrYY
rrYy
wrinkled, yellow wrinkled, yellow
RrYy
round, yellow
Rryy
round, green
rrYy
Rryy
wrinkled, yellow wrinkled, green
Figure 7.1
7.2 Dihybrid Crosses
 The Tsar and Tsarina were both
heterozygotes for hair texture and eye
color.
 Due to random alignment of chromosomes
and independent assortment, they could
form the following gametes:
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7.2 Dihybrid Crosses
(a) One possible Metaphase I alignment
Two types of gametes
Tsarina
Cc Dd
Meiosis
Wavy
hair
Dark
eyes
(b) Another possible Metaphase I alignment
Two other types of gametes
Tsarina
Cc Dd
Meiosis
Wavy
hair
Dark
eyes
Copyright © 2010 Pearson Education, Inc.
Figure 7.2a–b
7.2 Dihybrid Crosses
 Their gametes could then potentially
produce the following offspring:
(c) Punnett square for the mating of the Tsar and the Tsarina
Tsar ccDd
(straight hair,
dark eyes)
Tsarina CcDd
(wavy hair,
dark eyes)
Possible types of eggs
Possible types of sperm
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cD
CcDD
Wavy hair
Dark eyes
CcDd
Wavy hair
Dark eyes
ccDD
Straight hair
Dark eyes
ccDd
Straight hair
Dark eyes
cd
CcDd
Wavy hair
Dark eyes
Ccdd
Wavy hair
Blue eyes
ccDd
Straight hair
Dark eyes
ccdd
Straight hair
Blue eyes
Figure 7.2c
Extensions to Mendel’s Laws.
Genetics is not as simple as Gregor Mendel concluded,
(one gene, one trait).
We know now that there is a range of dominance
and that genes can work together and interact.
Ex: Incomplete dominance:
When the F1 generation have an appearance in between the
phenotypes of the parents.
Ex: pink snapdragons offspring of red and white ones.
Another way to say it is
In incomplete dominance
Heterozygote phenotype is somewhere between that of
two homozygotes
In humans hypercholesterolemia shows incomplete
dominance.
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Incomplete dominance in carnations
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7.3 Extensions/modifications of Mendelian
Genetics
 Incomplete dominance: two copies of the
dominant allele are required to see the full
phenotype; heterozygote phenotype is
intermediate to the homozygotes (e.g.,
flower color in snapdragons)
Flower color in snapdragons
x
Red = RR
Copyright © 2010 Pearson Education, Inc.
=
White = rr
Pink = Rr
Figure 7.3
The Spectrum of Dominance
 Complete dominance occurs when
phenotypes of the heterozygote and dominant
homozygote are identical. Ex: having a widows
peak or freckles.
 In incomplete dominance, the phenotype of F1
hybrids is somewhere between the phenotypes
of the two parental varieties
 In codominance, two dominant alleles affect
the phenotype in separate, distinguishable
ways. Ex: blood group type AB.
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7.3 Extensions of Mendelian Genetics
 Codominance: neither allele is dominant to
the other; heterozygote shows both traits at
once (e.g., coat color in cattle)
Coat color in cattle
x
Red = R1R1
Copyright © 2010 Pearson Education, Inc.
=
White = R2R2
Roan = R1R2
(patchy red and white coat)
Figure 7.4
Co-Dominance and multiple alleles:
 Co-dominance in human blood types
 Non-identical alleles specify two phenotypes that
are both expressed in heterozygotes
 Having more than 2 alleles for a given trait and
both alleles show in the phenotype. No single
one is dominant over the other.

Example: ABO blood types
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7.3 Extensions of Mendelian Genetics
 Blood typing can be used to exclude
potential parents.
 ABO blood group as three alleles of one
gene:
 IA and IB are codominant to each other; i is
recessive to both other alleles.
 An individual will have two of these alleles.
 Possible genotypes and phenotypes (blood
types) are shown in the next slide.
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The red blood cell antigen is coded for by the gene I (for isohaemaglutinogen) which
has 3 alleles A,B and O
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7.3 Extensions of Mendelian Genetics
 Blood typing could not be
done on the decomposed
skeletal remains.
Red blood
cell phenotype
Type A
Red blood
cell genotype
I AI A or I Ai
Sugar A
Type B
I BI B or I Bi
Sugar B
Type AB
Sugars
A and B
Type O
Copyright © 2010 Pearson Education, Inc.
I AI B
ii
Figure 7.5
Real life problem:
 A woman is suing her ex-husband for child
support. She is blood group A (we don’t know if she is
homozygous or heterozygous) and her ex-husband is blood
group B. The child is blood group O. Could he be
the father of the child?
Copyright © 2010 Pearson Education, Inc.
Answer:
Mother could be either
heterozygous: AO or
homozygous AA
Father could be BO or
BB
Probability of child
being type O is one in
four or 25%
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A
O
AB
BO
AO
OO
Pleiotropy
 Most genes have multiple phenotypic effects, a
property called pleiotropy
For example, pleiotropic alleles are responsible
for the multiple symptoms of certain hereditary
diseases, such as cystic fibrosis, sickle-cell
disease and hemophilia
Pleiotropy:
One genes having many effects. Only one
gene affects an organism in many ways.
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Pleiotropic effects of the sickle-cell allele in a homozygote
Copyright © 2010 Pearson Education, Inc.
Great web sites to help you study
 http://www.biologymad.com/
 http://www.kumc.edu/gec/
 http://www.dnaftb.org/dnaftb/1/concept/
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Abundance of a gene in a population is
not related to dominance
Other dominant traits:
Polydactylism
Astigmatism, near,far sightedness
Hypertension
Migrane headaches
Hitchhikers thumb
Hypercholesterolemia
Tongue roller
Free earlobes
Dominant Traits
Recessive Traits
Freckles
No freckles
Widow’s peak
Straight hairline
Free earlobe
Attached earlobe
Figure 9.8 A
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Frequency of Dominant Alleles
 Dominant alleles are not necessarily more
common in populations than recessive alleles
For example, one baby out of 400 in the United
States is born with extra fingers or toes
 The allele for this extra fingers/toes is dominant
to the allele for the more common trait of five
digits
 In this example, the recessive allele is far more
prevalent than the dominant allele in the
population
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Dominant
Recessive
Coarse body hair
Male pattern baldness
Freckles
Astigmatism
Near or far sightedness
Normal hearing
Broad lips
Large eyes
Polydactilism
Feet with normal arches
Hypertension
Diabetes
Migraine headaches
Normal transport
Hypercholesterolemia (familial)
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Fine body hair
Baldness
Absence of freckles
Normal vision
Normal vision
Deafness
thin lips
small eyes
normal digits
flat feet
normal blood pressure
normal excretion of insulin
normal
cystic fibrosis
normal cholesterol levels
7.4 Sex Determination and Sex Linkage
 Prince Alexis suffered from hemophilia, the
inability to clot blood normally due to the
absence of a clotting factor.
 Gene for this clotting factor is on the X
chromosome.
 Alexis inherited the hemophilia allele from his
mother.
Copyright © 2010 Pearson Education, Inc.
Copyright © 2010 Pearson Education, Inc.
7.4 Sex Determination and Sex Linkage
Male
XY
 Humans have 22 pairs of
autosomes and one pair
of sex chromosomes
 Women: two X
chromosomes
 Men: one X and one Y
chromosome
Female
XX
Meiosis
X
Y
Possible sperm
X
X
Possible eggs
Fertilization
This zygote will
develop into a male.
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XY
XX
This zygote will
develop into a female.
Figure 7.6
 Some disorders caused by recessive alleles on
the X chromosome in humans:
 Color blindness
 Duchenne muscular dystrophy
 Hemophilia
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SEX LINKED TRAITS ARE THOSE CARRIED BY THE X
CHROMOSOME
 Red-Green color blindness
Inability to see those colors. Red and green look all
the same ,like gray
 Hemophilia Blood clotting disorder.
The clotting factor VIII is not made, individual can
bleed to death.
 Duchenne Muscular dystrophy
X linked recessive, gradual and progressive
destruction of skeletal muscles .
 Faulty teeth enamel
Extremely rare, X linked Dominant
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7.4 Sex Determination and Sex Linkage
 Sex-linked genes: genes located on the sex
chromosomes
 X-linked: located on the X chromosome
 Y-linked: located on the Y chromosome
 Males always inherit their X from their mother
 Males are more likely to express recessive Xlinked traits than females
 Only females can be carriers of X-linked
recessive traits.
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7.4 Sex Determination and Sex Linkage
(b) Hemophiliac male x Unaffected female
(a) Unaffected male x Carrier female
X HY
x
X HX h
X hY
XH
X HX H
Unaffected
female
Y
X HY
X hY
Unaffected Hemophiliac
male
male
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X HX h
Carrier
female
X HX H
Possible types of eggs
1
–
4
Unaffected
females
1
–
4
1
–
4
Carrier females
Hemophiliac
males
1
–
4 Unaffected
males
Possible types of sperm
Possible types of sperm
Possible types of eggs
x
Xh
X HX h
Carrier
female
Y
X HY
Unaffected
male
1
–
2
Carrier
females
1
–
2
Unaffected
males
Figure 7.8
7.4 Sex Determination and Sex Linkage
PLAY
Animation—X-Linked Recessive Traits
Copyright © 2010 Pearson Education, Inc.
Figure 7.10
What is the probability that the Russian Czar who was normal but married a hemophilia gene carrier
have a daughter with hemophilia? A son with hemophilia? A grandchild with hemophilia from one of his
daughters?
Czar :
Czarina:
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7.4 Sex Determination and Sex Linkage
 Early female
embryos randomly
inactivate one of
the X chromosomes
in each cell.
 Inactivation is
irreversible and
inherited during cell
division.
 It is caused by RNA
wrapping around
the X chromosome.
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Active X chromosome
Muscular
dystrophy gene
Inactive X chromosome
Xist RNA
Xist RNA gene
Hemophilia gene
2 red-green
color blindness
genes
Figure 7.9
7.4 Sex Determination and Sex Linkage
 Result is patches of tissue in adult female
with different X chromosomes active.
(a) Phenotype
Orange male
Black female
Tortoise shell female
x
=
Genotype
Allele for
orange fur
Allele for
black fur
(b) X inactivation
Early embryo
Random X
chromosome
inactivation
Mitosis
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Inactive X
chromosome
Active X
chromosome
Tortoiseshell cat
with patches of
orange and black
Mitosis
Figure 7.10
Pedigree Analysis
 A pedigree is a family tree that describes the
interrelationships of parents and children
across generations
 Inheritance patterns of particular traits can be
traced and described using pedigrees
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7.5 Pedigrees
 Pedigree: a family
tree, showing the
inheritance of traits
through several
generations
 Symbols commonly
used in pedigrees:
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Pedigree analysis symbols
Female
Male
Marriage or mating
Offspring in
birth order
(from left to right)
or
Affected individuals
or
Known or presumed
carriers
Figure 7.11
7.5 Pedigrees
 Pedigrees reveal
modes of
inheritance
 Pedigree for an
autosomal
dominant trait:
(a) Dominant trait: Polydactyly
pp
pp
Pp
pp
Pp
Pp
Pp
Two affected
parents can
have
unaffected
offspring.
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Pp
pp
pp
pp
Two unaffected
individuals
cannot have
affected offspring.
Figure 7.12a
7.5 Pedigrees
 Pedigree for an
autosomal
recessive trait:
(b) Recessive trait: Attached earlobes
Ff
FF
Ff
ff
ff
Ff
Ff
The recessive trait
can skip a generation
completely, producing
unaffected individuals.
Ff
Ff
Ff
Ff
ff
ff
ff
ff
ff
ff
Two affected individuals
have affected offspring.
Copyright © 2010 Pearson Education, Inc.
Figure 7.12b
LE 14-14a
Ww
ww
ww
Ww ww ww Ww
WW
or
Ww
Widow’s peak
Ww
Ww
ww
First generation
(grandparents)
Second generation
(parents plus aunts
and uncles)
Third
generation
(two sisters)
ww
No widow’s peak
PowerPoint lecture prepared by
Dominant trait (widow’s peak)
Steve McCommas
Southern Illinois State University
Copyright © 2010 Pearson Education, Inc.
7.5 Pedigrees
 Pedigree for an (c) Sex-linked trait: Muscular dystrophy
X-linked trait: Affected
offspring
are most
often male.
X DX D
X DY
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X DY
X DY
X DY
X DX D
Carrier
X DX d
X dY
X DX d
X DY
X DY
Figure 7.12c
7.5 Pedigrees
 Pedigree analysis
reveals that Queen
Victoria’s mother
must have had a
mutation for the
hemophilia allele,
which was
ultimately passed
on to Prince Alexis
Romanov.
Copyright © 2010 Pearson Education, Inc.
Princess
Victoria
Tsarina’s great-grandmother
underwent a mutation to the
clotting factor VIII gene in her
ovary during meiosis.
Tsarina’s grandmother—
first carrier of the
mutant allele.
Queen
Victoria
Alice
(Tsarina’s mother)
Irene
(Tsarina’s
sister)
Waldemar
Leopold
(Tsarina’s
uncle)
Fred Tsarina
(Tsarina’s
brother)
Henry
Tsarina’s nephews
Tsarina’s daughters are
all possible carriers.
Son Alexis
had hemophilia.
Figure 7.13
 DNA recombination or genetic engineering is
the direct manipulation of genes for practical
purposes
 DNA and Crime Scene Investigations
 DNA fingerprinting has provided a powerful tool
for crime scene investigators
 DNA is isolated from biological fluids left at a
crime scene
 The technique determines with near certainty
whether two samples of DNA are from the
same individual
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7.6 DNA Fingerprinting
 No two individuals are genetically identical
(except for MZ twins)
 Small differences in nucleotide sequences of
their DNA
 This is the basis for DNA fingerprinting
 Unambiguous identification of people
Copyright © 2010 Pearson Education, Inc.
7.6 DNA Fingerprinting
 Steps in DNA fingerprinting:
 DNA isolated from tissue sample
 DNA cut into fragments with enzymes
 DNAs of different sequences produce
fragments of different sizes
 Fragments separated on basis of size and
visualized
 Each person’s set of fragments is unique
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The tools of DNA fingerprinting
 Restriction enzymes (used to cut DNA fragments to do
gel electrophoresis),
 PCR ( polymerase chain reaction)(used to
make copies of DNA when there isn’t
enough)
 Taq polymerase enzyme (used to put together a copy
of the DNA)
 Variable number tandem repeats (vntr)
 Gel electrophoresis- used to separate the
fragments
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7.6 DNA Fingerprinting
 Small amounts of DNA can be amplified
using PCR (polymerase chain reaction)
 DNA is mixed with nucleotides, specific
primers, Taq polymerase, and then is
heated
 Heating splits the DNA molecules into two
complementary strands
 Taq polymerase builds a new
complementary strand
 DNA is heated again, splitting the DNA
and starting a new cycle.
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12.10 DNA Fingerprinting
1st-The DNA molecule is cut with restriction enzymes
2nd- we have to separate the fragments
This is done by a technique called gel electrophoresis
The DNA is placed on a tray filled with gel through
which an electric current runs causing the fragments
to move through the gel. The segments separate by
how far they move in the gel according to size.
The DNA will form bands corresponding to the bases
(and no two people have the same sequence of bases) in
the gel which are unique for each individual. This is
DNA fingerprinting
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7.6 DNA Fingerprinting
PLAY
Animation—Polymerase Chain Reaction (PCR)
Copyright © 2010 Pearson Education, Inc.
7.6 DNA Fingerprinting
 DNA is cut into
fragments using
restriction enzymes,
which cut around
DNA sequences
called VNTRs
(variable number
tandem repeats)
Variable
number
tandem
repeat
(VNTR)
=
4 VNTRs
5 VNTRs
Student 1
6 VNTRs
3 VNTRs
Student 2
Homologous
chromosomes
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Figure 7.15
Restriction Enzymes
 Enzymes are used to "cut and paste" DNA
 DNA from two sources cut by restriction enzyme
at specific restriction sites
 Resulting restriction fragments contain a doublestranded sequence of DNA with
single-stranded "sticky ends"
 Fragments pair at their sticky ends by hydrogen
bonding
 DNA ligase pastes the strand into a recombinant
DNA molecule
Copyright © 2010 Pearson Education, Inc.
7.6 DNA Fingerprinting
 Gel electrophoresis separates DNA
fragments on basis of their sizes
 Electric current is applied to an agarose gel
 Smaller fragments run faster through the gel
 Fragments are transferred to a sheet of
filter paper
 Labeled radioactive probe reveals
locations of fragments containing VNTRs
(variable number tandem repeats)
 These steps are illustrated in the next slide
Copyright © 2010 Pearson Education, Inc.
7.6 DNA Fingerprinting
Copyright © 2010 Pearson Education, Inc.
Figure 7.16
12.10
Gel electrophoresis sorts DNA
molecules by size
Mixture of DNA
molecules of
different sizes
–
–
Longer
molecules
Power
source
Gel
+
Shorter
molecules
+
Figure 12.10
Copyright © 2010 Pearson Education, Inc.
Completed gel
7.6 DNA Fingerprinting
 Each person will have a
unique pattern of bands.
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Figure 7.17
7.6 DNA Fingerprinting
 DNA fingerprinting showed that 9 persons
were buried in the Ekaterinburg grave.
 Romanovs would be more similar in
pattern to each other than to nonrelatives.
 All of a child’s bands must be present in
one or both of the parents.
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7.6 DNA Fingerprinting
Adult
1
Adult
2
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Adult
3
Adult
4
Adult
5
Adult
6
Child
1
Child
2
Child
3
Figure 7.18
7.6 DNA Fingerprinting
 Pedigree of Romanov family
DNA evidence
Tsar’s
brother
George
Tatiana
Olga
Tsar
Maria
Tsarina
Carrier of
hemophilia
allele
Anastasia
Tsarina’s
sister
Not a carrier
of hemophilia
allele
Alexis
Hemophilia
Tsarina’s
niece Alice
Members of Romanov family executed in 1918
DNA evidence
Tsarina’s
grandnephew
Prince Philip
Lady Diana
William
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Charles
Henry
Anne
Peter
Timothy
Lawrence
Zara
Andrew
Sarah
Ferguson
Beatrice Eugenie
Queen
Elizabeth II
Edward
Sophie
Rhys-Jones
Louise
Figure 7.20
7.6 DNA Fingerprinting
 To see if parents and their children were
Romanovs, DNA fingerprints were
prepared for relatives of tsar and tsarina.
 Adult male skeleton (related to the
children) was related to George, the tsar’s
brother.
 Adult female skeleton (related to the
children) was related to Prince Philip, the
tsarina’s grand-nephew.
 Conclusion: the grave contained the tsar,
tsarina, three of their children, and four
servants.
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DNA and Crime Scene Investigations
 Many violent crimes go unsolved
For lack of enough evidence
 If biological fluids are left at a crime scene
DNA can be isolated from them
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Defendant’s
blood (D)
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Blood from defendant’s
clothes
Victim’s
blood (V)
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How Restriction Fragments Reflect DNA
Sequence
 Restriction fragment length polymorphisms
(RFLPs)

Reflect differences in the sequences of DNA
samples
Crime scene
Suspect
w
Cut
C
C
G
G
G
G
C
C
z
A
C
G
G
T
G
C
C
C
C
G
G
G
G
C
C
x
Cut
y
Figure 12.11A
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C
C
G
G
G
G
C
C
Cut
y
DNA from chromosomes
7.6 DNA Fingerprinting
 Each cycle, the amount of DNA doubles.
Primer
1 PCR is used to
amplify, or make
copies of, DNA.
During a PCR
reaction, primers
(free nucleotides)
and DNA are mixed
with heat-tolerant
polymerase.
2 The DNA is heated
to separate, or
denature, the two
strands.
Double stranded DNA
4 A copy of the
DNA template is
assembled.
Primer
Polymerase
5 The mixture is
heated again. The
process is repeated
many times,
doubling the DNA
amount each time.
3 As the mixture
cools, the primers
bond to the DNA
template and the
two polymerase
use the primers to
initiate synthesis.
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Figure 7.14
 Detecting a harmful allele using restriction
fragment analysis
1 Restriction fragment
preparation
I
II
III
Restriction
fragments
2 Gel electrophoresis
I
II III
3 Blotting
Filter paper
4 Radioactive probe
Radioactive, singlestranded DNA (probe)
Probe
I
5 Detection of radioactivity
II
III
(autoradiography)
Film
I
Figure 12.11C
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II
III