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Chapter 7
 DNA Detective
 Complex Patterns of Inheritance and DNA
Fingerprinting
Copyright © 2010 Pearson Education, Inc.
Chapter 7
Section 1 – Forensic Science
Section 2 – Dihybrid Crosses
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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?
Copyright © 2010 Pearson Education, Inc.
7.1 Forensic Science
Forensic Science
The study of evidence discovered at a crime
scene and used in a court of law.
 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 heterozygotes
for eye color (Dd).
 For hair texture, the Tsar was homozygous
recessive (cc) and Tsarina were
heterozygous (Cc)
 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
Chapter 7
End Section 1 – Forensic Science
End Section 2 – Dihybrid Crosses
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Chapter 7 Section 3
Extensions to Mendelian Genetics
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7.3 Extensions of Mendelian Genetics
Extensions of Mendelian Genetics
 More complex patterns of inheritance
 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
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Red = RR
=
White = rr
Pink = Rr
Figure 7.3
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)
 Polygenic Traits = affected by multiple
genes and the environment
 Height, weight, etc
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Figure 7.4
7.3 Extensions of Mendelian Genetics
 Blood typing can be used to
exclude potential parents.
 ABO blood group has three
alleles of one gene:
 Multiple allelism
 IA and IB are codominant to each
other; i is recessive to both other
alleles.
 An individual will have two of
these alleles.
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7.3 Extensions of Mendelian Genetics
 Blood typing with Rh factor
 A RBC membrane protein
 Simple mendelian two gene complete dominance
 Indicated as + or – after ABO blood type
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7.3 Extensions of Mendelian Genetics
 Blood Transfusions
 O- is universal donor
 AB+ is universal receiver
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End Chapter 7 Section 3
Extensions to Mendelian Genetics
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Chapter 7 Section 4
Sex Determination and Sex Linkage
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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.
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7.4 Sex Determination and Sex Linkage
Sex Determination and
Sex Linkage
 Humans have 22 pairs of
autosomes and one pair
of sex chromosomes
 Women: two X
chromosomes
 Men: one X and one Y
chromosome
Male
XY
Meiosis
X
Y
Possible sperm
X
X
Possible eggs
Fertilization
This zygote will
develop into a male.
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Female
XX
XY
XX
This zygote will
develop into a female.
Figure 7.6
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 X-linked
traits than females
 Only females can be carriers of X-linked recessive
traits.
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7.4 Sex Determination and Sex Linkage
Crosses of carriers for hemophilia
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Figure 7.8
7.4 Sex Determination and Sex Linkage
Other X-linked recessive traits
•Red-Green Color Blindness
•Duchenne muscular dystrophy
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Figure 7.8
7.4 Sex Determination and Sex Linkage
X Inactivation
 Early female embryos
randomly inactivate one
of the X chromosomes in
each cell.
 Inactivation is irreversible
and inherited during
mitotic cell division.
 It is caused by RNA
wrapping around the X
chromosome.
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Figure 7.9
7.4 Sex Determination and Sex Linkage
Tortoiseshell Cats
 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
7.4 Sex Determination and Sex Linkage
Y-Link Genes
 Passed only from father to son
 But few genes on Y-chromosome
 SRY gene
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7.4 Sex Determination and Sex Linkage
PLAY
Animation—X-Linked Recessive Traits
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Figure 7.10
End Chapter 7 Section 4
Sex Determination and Sex Linkage
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Chapter 7 Section 5
Pedigrees
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7.5 Pedigrees
Pedigree: a family
tree, showing the
inheritance of traits
through several
generations
 Pedigrees reveal
modes of
inheritance
 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
Pedigree for an autosomal dominant trait:
(a) Dominant trait: Polydactyly
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:
Attached earlobes
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Figure 7.12b
7.5 Pedigrees
Pedigree for an X-linked trait: Muscular
dystrophy
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Figure 7.12c
7.5 Pedigrees
Romanov Pedigree
 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.
Figure 7.13
End Chapter 7 Section 5
Pedigrees
Copyright © 2010 Pearson Education, Inc.
Chapter 7 Section 6
DNA Fingerprinting
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7.6 DNA Fingerprinting
DNA Fingerprinting
 No two individuals are genetically identical
(except for MonoZygotic twins)
 Therefore, individuals have small differences
in nucleotide sequences of their DNA
 This is the basis for DNA fingerprinting
 Unambiguous identification of people
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7.6 DNA Fingerprinting
Steps in DNA fingerprinting: overview
1. DNA isolated from tissue sample
 Small samples can be amplified using
another technique called “PCR”
2. DNA cut into fragments with enzymes
 DNAs of different sequences produce
fragments of different sizes
3. Fragments separated on basis of size and
visualized
4. Each person’s set of fragments is unique
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7.6 Polymerase Chain Reaction
DNA Fingerprinting: using small samples
1. Small amounts of DNA can be amplified
using PCR (polymerase chain reaction)
2. DNA is mixed with nucleotides, specific
primers, Taq polymerase, and then is
heated
3. Heating splits the DNA molecules into two
complementary strands
4. As solution cools, Taq polymerase builds
a new complementary strand
5. DNA is heated again, splitting the DNA
and starting a new cycle.
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7.6 Polymerase Chain Reaction
 In each cycle of PCR, the 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.
Double stranded DNA
4 A copy of the
DNA template is
assembled.
Primer
2 The DNA is heated
to separate, or
denature, the two
strands.
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
7.6 DNA Fingerprinting
PLAY
Animation—Polymerase Chain Reaction (PCR)
Copyright © 2010 Pearson Education, Inc.
7.6
DNA Fingerprinting
Cut DNA into fragments
 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
7.6 DNA Fingerprinting
DNA Fingerprint
 Gel electrophoresis
separates DNA fragments
on basis of their sizes
 Each person will have a
unique pattern of bands.
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Figure 7.17
7.6 DNA Fingerprinting
Romanovs DNA fingerprinting analysis
 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
Hypothetical DNA pattern from Romanov graves
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Figure 7.18
7.6 DNA Fingerprinting
Pretenders to the Romanov throne
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Figure 7.18
7.6 DNA Fingerprinting
But were remains in grave really Romanovs?
 To see if parents and their children were
Romanovs, DNA fingerprints were
prepared for relatives of tsar and tsarina.
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7.6 DNA Fingerprinting
Pedigree of Romanov family
DNA evidence
Tsar’s
brother
George
Olga
Tatiana
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
Beatrice
Sarah
Ferguson
Eugenie
Queen
Elizabeth II
Edward
Sophie
Rhys-Jones
Louise
Figure 7.20
7.6 DNA Fingerprinting
But were remains in grave really Romanovs?
 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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End Chapter 7 Section 6
DNA Fingerprinting
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End Chapter 7
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