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Chapter 6
DNA Detective
Complex Patterns of Inheritance,
and DNA Fingerprinting
Fourth Edition
BIOLOGY
Science for Life | with Physiology
Colleen Belk • Virginia Borden Maier
© 2013 Pearson Education, Inc.
Copyright © 2009 Pearson Education, Inc.
PowerPoint Lecture prepared by
Jill Feinstein
Richland Community College
1 Extensions of Mendelian Genetics
 Incomplete Dominance is when a heterozygote
expresses a phenotype intermediate between both
alleles.
 For example, RR produces red flowers, Rr produces
pink flowers and rr produces white flowers
 Codominance is when two alleles are expressed at
the same time.
 ABO blood type is an example of this with both the
dominant A and B being expressed in a type AB person.
 Multiple allelism occurs when there are more than
two alleles of a gene.
 ABO blood types exhibit this.
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1 Extensions of Mendelian Genetics
 ABO blood group has 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.
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1 Extensions of Mendelian Genetics
 Another blood group is called the Rh factor.
 Rh+ is caused by a dominant allele.
 Rh+Rh+ or Rh+Rh-
 Rh- is caused by 2 recessive alleles.
 Rh-Rh-
 Blood typing can be used to exclude potential
parents.
 E.g., an AB parent can never have an O child and
two Rh- parents can never have a Rh+ child.
 See Table 8.2 for compatibilities of blood types.
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1 Extensions of Mendelian Genetics
 Pleiotropy is the ability of a single gene to
cause multiple effects on the individual’s
phenotype.
 Hemophilia is an example of pleiotropy.
 The inability to clot blood normally due to the
absence of a clotting factor
 Gene for this clotting factor is on the X
chromosome
 Prince Alexis suffered from this and inherited the
hemophilia allele from his mother
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2 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
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2 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
 SRY gene which leads to the development of the
testes
 Males always inherit their X from their mother
 Males are more likely to express recessive X-linked
traits than females due to carrying only 1 X.
 Females are less likely to express X-linked traits
since they have to have 2 copies of the bad X’s.
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2 Sex Determination and Sex Linkage
 Only females can be carriers of X-linked recessive
traits.
 Carriers express the normal trait but are heterozygous,
so they carry the allele for the recessive trait.
 Hemophilia, red-green color blindness, and Duchenne
Muscular dystrophy are example of X-linked traits.
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2 Sex Determination and Sex Linkage
 X inactivation guarantees
that all females receive only
1 dose of the proteins by
the X chromosomes.
 Inactivation is irreversible
and inherited during cell
division.
 It is caused by RNA
wrapping around the X
chromosome.
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Animation: X-Linked Recessive Traits
Click “Go to Animation” / Click “Play”
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3 Pedigrees
 Pedigree: a family tree,
showing the inheritance
of traits through several
generations
 Symbols commonly
used in pedigrees are
circles and squares
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3 Pedigrees
 Pedigrees reveal
modes of inheritance
 Pedigree for
an autosomal
dominant trait:
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3 Pedigrees
 Pedigree for an autosomal recessive trait:
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3 Pedigrees
 Pedigree for an X-linked trait:
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3 Pedigrees
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4 DNA Fingerprinting
 No two individuals are genetically identical except
for identical twins.
 Small differences in nucleotide sequences of their
DNA
 This is the basis for DNA fingerprinting
 Unambiguous identification of people
 When sample size is small it is necessary to copy the
genetic material to increase the quantity available for
testing.
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4 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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4 DNA Fingerprinting
 Each cycle, the amount of DNA doubles.
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Animation: Polymerase Chain Reaction (PCR)
Click “Go to Animation” / Click “Play”
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4 DNA Fingerprinting
 DNA is cut into
fragments using
restriction enzymes,
which cut around DNA
sequences called
VNTRs (variable
number tandem
repeats).
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4 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 probe reveals locations of fragments
containing VNTRs
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4 DNA Fingerprinting
 Each person’s set of fragments is unique.
 All of a child’s bands must be present in one
or both of the parents.
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4 DNA Fingerprinting
 Pedigree of Romanov family
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4 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 grandnephew.
 Conclusion: the grave contained the tsar, tsarina,
three of their children, and four servants.
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Which forensic technique was used to determine
the identity of the Romanovs?

examining fingerprints

ballistic (firearm) evidence

DNA fingerprinting

toxicology
© 2013 Pearson Education, Inc.
Which forensic technique was used to determine
the identity of the Romanovs?

examining fingerprints

ballistic (firearm) evidence

DNA fingerprinting

toxicology
© 2013 Pearson Education, Inc.
Snapdragon color is an example of incomplete
dominance. If you cross a red snapdragon with a
white snapdragon, what will the offspring look like?

All of the offspring will be red.

All of the offspring will be white.

All of the offspring will be pink.

Half the offspring will be red and half will be white.
© 2013 Pearson Education, Inc.
Snapdragon color is an example of incomplete
dominance. If you cross a red snapdragon with a
white snapdragon, what will the offspring look like?

All of the offspring will be red.

All of the offspring will be white.

All of the offspring will be pink.

Half the offspring will be red and half will be white.
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Coat color of cattle displays codominance.
A red coated cattle is bred with a white
coated cattle. What color coat will their offspring
have?

Red coat
C. Pink coat

White coat
D. Red and white coat
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Coat color of cattle displays codominance.
A red coated cattle is bred with a white
coated cattle. What color coat will their offspring
have?

Red coat
C. Pink coat

White coat
D. Red and white coat
© 2013 Pearson Education, Inc.
Which genetic term best describes how the ABO
blood system is inherited?

codominance

incomplete dominance

pleiotropy

X-inactivation
© 2013 Pearson Education, Inc.
Which genetic term best describes how the ABO
blood system is inherited?

codominance

incomplete dominance

pleiotropy

X-inactivation
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Who is more likely to suffer from colorblindness, a
disorder caused by a recessive allele on the Xchromosome?

males

females

babies

the elderly
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Who is more likely to suffer from colorblindness, a
disorder caused by a recessive allele on the Xchromosome?

males

females

babies

the elderly
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Which of the following disorders is carried on
the X chromosome and is considered
pleiotrophic?

Huntington's disease

Cystic Fibrosis

Hemophilia

Tay-Sachs
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Which of the following disorders is carried on
the X chromosome and is considered
pleiotrophic?

Huntington's disease

Cystic Fibrosis

Hemophilia

Tay-Sachs
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What type of trait does this pedigree show?

recessive trait

sex-linked trait

dominant trait

codominant trait
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What type of trait does this pedigree show?

recessive trait

sex-linked trait

dominant trait

codominant trait
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Why is Taq polymerase used instead of human
DNA polymerase?

Taq polymerase is resistant to high
temperatures.

Taq polymerase is resistant to high pH levels.

Taq polymerase is resistant to low
temperatures.

Taq polymerase is resistant to low pH levels.
© 2013 Pearson Education, Inc.
Why is Taq polymerase used instead of human
DNA polymerase?

Taq polymerase is resistant to high
temperatures.

Taq polymerase is resistant to high pH levels.

Taq polymerase is resistant to low
temperatures.

Taq polymerase is resistant to low pH levels.
© 2013 Pearson Education, Inc.
Gel electrophoresis separates DNA fragments
based on _______.

Shape

pH

Number of strands

Size
© 2013 Pearson Education, Inc.
Gel electrophoresis separates DNA fragments
based on _______.

Shape

pH

Number of strands

Size
© 2013 Pearson Education, Inc.
______ is used to amplify DNA.

PCR

Gel electrophoresis

RFLP

VNTR
© 2013 Pearson Education, Inc.
______ is used to amplify DNA.

PCR

Gel electrophoresis

RFLP

VNTR
© 2013 Pearson Education, Inc.