© 2013 Pearson Education, Inc.Lectures by Edward J. Zalisko
PowerPoint® Lectures forCampbell Essential Biology, Fifth Edition, and
Campbell Essential Biology with Physiology,
Fourth Edition– Eric J. Simon, Jean L. Dickey, and Jane B. Reece
Chapter 9Chapter 9Patterns of Inheritance
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• People have selected and mated dogs with
preferred traits for more than 15,000 years.
• Over thousands of years, such genetic tinkering
has led to the incredible variety of body types
and behaviors in dogs today.
• The biological principles underlying genetics
have only recently been understood.
Biology and Society: Our Longest-Running Genetic Experiment: Dogs
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Figure 9.0 3
• Heredity is the transmission of traits from one
generation to the next.
• Genetics is the scientific study of heredity.
• Gregor Mendel
– worked in the 1860s,
– was the first person to analyze patterns of inheritance, and
– deduced the fundamental principles of genetics.
HERITABLE VARIATION AND PATTERNS OF INHERITANCE
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In an Abbey Garden
• Mendel studied garden peas because they
– were easy to grow,
– came in many readily distinguishable varieties,
– are easily manipulated, and
– can self-fertilize.
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5 Figure 9.2
Carpel(produces eggs)
Stamen(makes sperm-producingpollen)
Petal
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Figure 9.3-1
Removedstamensfrom purpleflower.
Stamens
Transferred pollen fromstamens of white flower
to carpel of purple flower.
Parents
(P)
Carpel
2
1
7 Figure 9.3-2
Removedstamensfrom purpleflower.
Stamens
Transferred pollen fromstamens of white flower
to carpel of purple flower.
Parents
(P)
Carpel
Pollinated carpel
matured into pod.
3
2
1
8
Figure 9.3-3
Removedstamensfrom purpleflower.
Stamens
Transferred pollen fromstamens of white flower
to carpel of purple flower.
Parents
(P)
Carpel
Offspring
(F1)
Pollinated carpel
matured into pod.
Planted seeds
from pod.
4
3
2
1
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• A character is a heritable feature that varies
among individuals.
• A trait is a variant of a character.
• Each of the characters Mendel studied occurred in
two distinct traits.
In an Abbey Garden
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• Mendel
– created purebred varieties of plants and
– crossed two different purebred varieties.
In an Abbey Garden
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• Hybrids are the offspring of two different
purebred varieties.
– The parental plants are the P generation.
– Their hybrid offspring are the F1 generation.
– A cross of the F1 plants forms the F2 generation.
In an Abbey Garden
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Mendel’s Law of Segregation
• Mendel performed many experiments.
• He tracked the inheritance of characters that occur
as two alternative traits.
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13 Figure 9.4
WhitePurple
RecessiveDominant
Green Yellow
Terminal Axial
Wrinkled Round
Green Yellow
Seed shape
Seed color
Flower position
Flower color
Pod color
RecessiveDominant
Pod shape
Stem length
Inflated Constricted
Tall Dwarf
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Figure 9.4a 15Monohybrid Crosses
• A monohybrid cross is a cross between purebred
parent plants that differ in only one character.
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Figure 9.5-1
Purple flowers
White flowers
P Generation(purebredparents)
17 Figure 9.5-2
Purple flowers
F1 Generation
White flowers
P Generation(purebredparents)
All plants havepurple flowers
18
Figure 9.5-3
Purple flowers
F1 Generation
White flowers
P Generation(purebredparents)
All plants havepurple flowers
F2 Generation
Fertilizationamong F1 plants(F1 ×××× F1)
of plants
have purple flowers
of plants
have white flowers
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14
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• Mendel developed four hypotheses from the
monohybrid cross, listed here using modern
terminology (including “gene” instead of “heritable
factor”).
1. The alternative versions of genes are called alleles.
Monohybrid Crosses
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2. For each inherited character, an organism inherits two alleles, one from each parent.
– An organism is homozygous for that gene if both
alleles are identical.
– An organism is heterozygous for that gene if the
alleles are different.
Monohybrid Crosses
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3. If two alleles of an inherited pair differ,
– then one determines the organism’s appearance
and is called the dominant allele and
– the other has no noticeable effect on the organism’s
appearance and is called the recessive allele.
Monohybrid Crosses
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4. Gametes carry only one allele for each inherited character.
– The two alleles for a character segregate (separate)
from each other during the production of gametes.
– This statement is called the law of segregation.
Monohybrid Crosses
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• Do Mendel’s hypotheses account for the 3:1 ratio
he observed in the F2 generation?
• A Punnett square highlights
– the four possible combinations of gametes and
– the four possible offspring in the F2 generation.
Monohybrid Crosses
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• Geneticists distinguish between an organism’s
physical appearance and its genetic makeup.
– An organism’s physical appearance is its phenotype.
– An organism’s genetic makeup is its genotype.
Monohybrid Crosses
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25 Figure 9.6P Generation Genetic makeup (alleles)
Alleles carried by parents
Gametes
Purple flowersPP
White flowerspp
All P All p
pP
F1 Generation(hybrids)
F2 Generation(hybrids)
Allelessegregate
Gametes
Purple flowersAll Pp
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21
Sperm fromF1 plant
Eggs fromF1 plant
Phenotypic ratio3 purple : 1 white
Genotypic ratio1 PP : 2 Pp : 1 pp
p
p
P
PPP Pp
Pp pp
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Blast Animation: Single-Trait Crosses
Select “Play”
27 Genetic Alleles and Homologous Chromosomes
• A gene locus is a specific location of a gene along
a chromosome.
• Homologous chromosomes have alleles (alternate
versions) of a gene at the same locus.
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Figure 9.7
Homologouschromosomes
P
Genotype:
Gene loci
P
a
aa
b
B
Dominantallele
Recessive allele
BbPP
Homozygousfor thedominant allele
Homozygousfor therecessive allele
Heterozygouswith one dominantand one recessiveallele
a
29 Mendel’s Law of Independent Assortment
• A dihybrid cross is the mating of parental
varieties differing in two characters.
• What would result from a dihybrid cross? Two
hypotheses are possible:
1. dependent assortment or
2. independent assortment.
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© 2013 Pearson Education, Inc.
Blast Animation: Two-Trait Crosses
Select “Play”
31 Figure 9.8
F1 Generation
F2 Generation
RRYY
Predicted results(not actually seen)
P Generation
Gametes RY
rryy
ry
(a) Hypothesis: Dependent assortment
RrYy
RY ry
Sperm
EggsEggs
RY
ry
Actual results(support hypothesis)
RRYY
RY
rryy
ry
RrYy
(b) Hypothesis: Independent assortment
Gametes
RY ry
Sperm
RY
ry
Ry
rY
RyrY
RRYY
RryyRRyyRrYyRRYy
RrYy rrYy Rryy rryy
RrYY
RrYY rrYY RrYy rrYy
RRYy RrYy
Yellowround
Yellowwrinkled
Greenwrinkled
Greenround
16
1
16
3
16
3
16
9
4
1
4
1
4
1
4
1
4
1
4
1
4
1
4
1
2
1
2
1
2
1
2
1
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• Mendel’s dihybrid cross supported the hypothesis
that each pair of alleles segregates independently
of the other pairs during gamete formation.
• Thus, the inheritance of one character has no
effect on the inheritance of another.
• This is called Mendel’s law of independent assortment.
• Independent assortment is also seen in two
hereditary characters in Labrador retrievers.
Mendel’s Law of Independent Assortment
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33 Figure 9.9Blind dog
Phenotypes
(a) Possible phenotypes of Labrador retrievers
B_N_
Blind dog
Genotypes
(b) A Labrador dihybrid cross
Black coat,
normal visionB_nn
Black coat,
blind (PRA)bbnn
Chocolate coat,blind (PRA)
bbN_
Chocolate coat,
normal vision
Mating of double heterozygotes
(black coat, normal vision)
BbNn BbNn
Phenotypicratio ofoffspring
9 black coat,
normal vision
3 black coat,
blind (PRA)
3 chocolate coat,
normal vision1 chocolate coat,
blind (PRA)
Blind Blind
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Figure 9.9a
Blind
Blind
Mating of double hererozygotes(BbNn ×××× BbNn)
9 black coat,normal vision
3 black coat,blind (PRA)
3 chocolate coat,normal vision
1 chocolate coat,blind (PRA)
35 Using a Testcross to Determine an Unknown Genotype
• A testcross is a mating between
– an individual of dominant phenotype (but unknown genotype) and
– a homozygous recessive individual.
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Figure 9.10
Two possible genotypes for the black dog:
B_ bb
Testcross
Genotypes
Bb
B b
orBB
B
b Bb Bb bbb
Gametes
Offspring All black 1 black : 1 chocolate
37 The Rules of Probability
• Mendel’s strong background in mathematics
helped him understand patterns of inheritance.
• The rule of multiplication states that the
probability of a compound event is the product of
the separate probabilities of the independent
events.
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Figure 9.11
F1 Genotypes
F2 Genotypes
Bb female Bb male
Formation of eggs Formation of sperm
Malegametes
Fem
ale
gam
ete
s
2
1
2
1
2
1
2
1
2
1
2
14
1
4
1
4
1
4
1
( ×××× )
B
BB B B
B
b
b
b b b b
39 Family Pedigrees
• Mendel’s principles apply to the inheritance of
many human traits.
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Figure 9.12
DO
MIN
AN
T T
RA
ITS
Free earlobe
RE
CE
SS
IVE
TR
AIT
S
Widow’s peakFreckles
Attached earlobeStraight hairlineNo freckles
41 Figure 9.12a
Freckles No freckles
42
Figure 9.12b
Widow’s peak Straight hairline
43 Figure 9.12c
Free earlobe Attached earlobe
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• Dominant traits are not necessarily
– normal or
– more common.
• Wild-type traits are
– those seen most often in nature and
– not necessarily specified by dominant alleles.
Family Pedigrees
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• A family pedigree
– shows the history of a trait in a family and
– allows geneticists to analyze human traits.
Family Pedigrees
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Figure 9.13
Female Male
Attached Free
Female Male
First generation(grandparents)
Second generation(parents, aunts, anduncles)
Third generation(brother andsister)
AaronFf
BettyFf
Cletusff
DebraFf
EvelynFForFf
LisaFForFf
Fredff
Gabeff
HalFf
InaFf
Jillff
Kevinff
50 Human Disorders Controlled by a Single Gene
• Many human traits
– show simple inheritance patterns and
– are controlled by single genes on autosomes.
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Table 9.1 52 Recessive Disorders
• Most human genetic disorders are recessive.
• Individuals who have the recessive allele but
appear normal are carriers of the disorder.
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Figure 9.14
Parents
Offspring
DdHearing Hearing
Dd
Sperm
Eggs
D
HearingD
Dd
d
Hearing
(carrier)
DD
DdHearing
(carrier)
dd
Deafd
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• Cystic fibrosis is
– the most common lethal genetic disease in the United States and
– caused by a recessive allele carried by about one in 31 Americans.
Recessive Disorders
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• Prolonged geographic isolation of certain
populations can lead to inbreeding, the mating of
close relatives.
• Inbreeding increases the chance of offspring that
are homozygous for a harmful recessive trait.
Recessive Disorders
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56 Dominant Disorders
• Some human genetic disorders are dominant.
– Achondroplasia is a form of dwarfism.
– The homozygous dominant genotype causes
death of the embryo.
– Thus, only heterozygotes have this disorder.
– Huntington’s disease, which leads to degeneration of the nervous system, does not usually begin until middle age.
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Figure 9.15 58 Figure 9.16
Parents
Sperm
Eggs
d
DwarfD
Dd
d
Dd
ddd
Normal
(no achondroplasia) Molly JoDwarf
(achondroplasia)Dddd
Normaldd
Normal
DwarfMatt AmyJacob Zachary
Jeremy
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Genetic Testing
• Today many tests can detect the presence of
disease-causing alleles.
• Most genetic tests are performed during
pregnancy.
– Amniocentesis collects cells from amniotic fluid.
– Chorionic villus sampling removes cells from placental tissue.
• Genetic counseling helps patients understand the
results and implications of genetic testing.
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