Chapter 9

Report
Chapter 9
Patterns of Inheritance
PowerPoint Lectures for
Biology: Concepts and Connections, Fifth Edition
– Campbell, Reece, Taylor, and Simon
Lectures by Chris Romero
Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings
Purebreds and Mutts–A Difference of Heredity
• Purebred dogs
– Are very similar on a genetic level due to
selective breeding
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• Mutts, or mixed breed dogs on the other hand
– Show considerably more genetic variation
Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings
MENDEL’S LAWS
9.1 The science of genetics has ancient roots
• The historical roots of genetics, the science of
heredity
– Date back to ancient attempts at selective
breeding
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9.2 Experimental genetics began in an abbey
garden
• Modern genetics
– Began with Gregor Mendel’s quantitative
experiments with pea plants
Petal
Stamen
Carpel
Figure 9.2 A
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Figure 9.2 B
• Mendel crossed pea plants that differed in
certain characteristics
– And traced traits from generation to
generation
1 Removed stamens
from purple
flower
White
Stamens
Carpel
Parents
(P)
2 Transferred
pollen from stamens
Purple of white flower to
carpel of purple flower
3 Pollinated carpel
matured into pod
4 Planted seeds
from pod
Offspring
(F1)
Figure 9.2 C
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• Mendel hypothesized that there are alternative
forms of genes
– The units that determine heritable traits
Flower color
White
Axial
Terminal
Seed color
Yellow
Green
Seed shape
Round
Wrinkled
Pod shape
Inflated
Constricted
Pod color
Green
Yellow
Tall
Dwarf
Flower position
Figure 9.2 D
Purple
Stem length
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9.3 Mendel’s law of segregation describes the
inheritance of a single characteristic
• From his experimental data
– Mendel deduced that an organism has two
genes (alleles) for each inherited characteristic
P generation
(true-breeding
parents)

Purple flowers
F1 generation
White flowers
All plants have
purple flowers
Fertilization
among F1 plants
(F1  F1)
F2 generation
3
1
4 of plants
4 of plants
have purple flowers have white flowers
Figure 9.3 A
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• For each characteristic
– An organism inherits two alleles, one from
each parent
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• If the two alleles of an inherited pair differ
– Then one determines the organism’s
appearance and is called the dominant
allele
• The other allele
– Has no noticeable effect on the organism’s
appearance and is called the recessive
allele
Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings
• Mendel’s law of segregation
– Predicts that allele pairs separate from
each other during the production of
gametes
P plants
Genetic makeup (alleles)
pp
PP
Gametes
All p
All P
F1 plants
(hybrids)
All Pp
1P
2
Gametes
1p
2
Sperm
F2 plants Phenotypic ratio
3 purple : 1 white
Genotypic ratio
1 PP: 2 Pp: 1 pp
Figure 9.3 B
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P
p
P
PP
Pp
p
Pp
pp
Eggs
9.4 Homologous chromosomes bear the two
alleles for each characteristic
• Alternative forms of a gene
– Reside at the same locus on homologous
Dominant
chromosomes
allele
Gene loci
P
P
a
B
a
b
Recessive
allele
Genotype:
Figure 9.4
PP
Homozygous
for the
dominant allele
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aa
Homozygous
for the
recessive allele
Bb
Heterozygous
9.5 The law of independent assortment is
revealed by tracking two characteristics at once
• By looking at two characteristics at once
– Mendel tried to determine how two
characteristics were inherited
Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings
• Mendel’s law of independent assortment
– States that alleles of a pair segregate independently
of other allele pairs during gamete formation
P generation
Hypothesis: Dependent assortment
RRYY
rryy
Hypothesis: Independent assortment
RRYY
ry
Gametes RY
rryy

Gametes RY
ry
RrYy
RrYy
F1 generation
Sperm
Sperm
1
2 RY
1
RY
2
F2 generation
1
1 ry
RY
4
4
1
2 ry
Eggs
1
ry
2
Actual results
contradict hypothesis
Figure 9.5 A
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1
RY
4
1
ry
4
Eggs
1
Ry
4
1
ry
4
1
RY
4
1 ry
4
RRYY
RrYY RRYy RrYy
RrYY
rrYY
RrYy
rrYy
RRYy
RrYy
RRyy
Rryy
RrYy
rrYy
Rryy
rryy
Actual results
support hypothesis
9
16
3
16
3
16
1
16
Yellow
round
Green
round
Yellow
wrinkled
Green
wrinkled
• An example of independent assortment
Blind
Blind
Phenotypes
Genotypes
Black coat, normal vision
B_N_
Black coat, blind (PRA) Chocolate coat, normal vision Chocolate coat, blind (PRA)
B_nn
bbN_
bbnn
Mating of heterozygotes
(black, normal vision)
Phenotypic ratio
of offspring
9 black coat,
normal vision
BbNn
3 black coat,
blind (PRA)
Figure 9.5 B
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
BbNn
3 chocolate coat,
normal vision
1 chocolate coat,
blind (PRA)
9.6 Geneticists use the testcross to determine unknown genotypes
• The offspring of a testcross, a mating between an individual of
unknown genotype and a homozygous recessive individual
– Can reveal the unknown’s genotype

Testcross:
Genotypes
bb
B_
Two possibilities for the black dog:
BB
Gametes
Bb
B
b
Offspring
or
Bb
All black
Figure 9.6
Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings
b
B
b
Bb
bb
1 black : 1 chocolate
9.7 Mendel’s laws reflect the rules of probability
• Inheritance follows the rules of probability
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• The rule of multiplication
– Calculates the probability of two independent events
• The rule of addition
– Calculates the probability of an event that can occur
in alternate ways
F genotypes
1
Bb male
Formation of sperm
Bb female
Formation of eggs
1
2
1
2
B
1
2
b
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B
B
b
1
4
B
b
1
4
b
B
1
4
F2 genotypes
Figure 9.7
1
2
B
b
b
1
4
CONNECTION
9.8 Genetic traits in humans can be tracked
through family pedigrees
• The inheritance of many human traits
– Follows Mendel’s laws
Dominant Traits
Recessive Traits
Freckles
No freckles
Widow’s peak
Straight hairline
Free earlobe
Attached earlobe
Figure 9.8 A
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• Family pedigrees
– Can be used to determine individual genotypes
Dd
Joshua
Lambert
D?
John
Eddy
Dd
Abigail
Linnell
dd
Jonathan
Lambert
D?
Abigail
Lambert
Dd
Dd
dd
D?
Hepzibah
Daggett
Dd
Elizabeth
Eddy
Dd
Dd
Dd
dd
Female Male
Deaf
Hearing
Figure 9.8 B
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CONNECTION
9.9 Many inherited disorders in humans are
controlled by a single gene
• Some autosomal disorders in humans
Table 9.9
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Recessive Disorders
• Most human genetic disorders are recessive
Parents
Normal
Dd

Normal
Dd
Sperm
D
D
Offspring
DD
Normal
d
Dd
Normal
(carrier)
Eggs
d
Figure 9.9 A
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Dd
Normal
(carrier)
dd
Deaf
Dominant Disorders
• Some human genetic disorders are dominant
Figure 9.9 B
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CONNECTION
9.10 New technologies can provide insight into one’s
genetic legacy
• New technologies
– Can provide insight for reproductive decisions
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Identifying Carriers
• For an increasing number of genetic disorders
– Tests are available that can distinguish
carriers of genetic disorders
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Fetal Testing
• Amniocentesis and chorionic villus sampling (CVS)
– Allow doctors to remove fetal cells that can be tested
for genetic abnormalities
Chorionic villus sampling (CVS)
Amniocentesis
Needle inserted
through abdomen to Ultrasound
extract amniotic fluid monitor
Ultrasound
monitor
Fetus
Fetus
Placenta
Uterus
Suction tube inserted
through cervix to extract
tissue from chorionic villi
Placenta
Chorionic
villi
Cervix
Cervix
Uterus
Amniotic
fluid
Centrifugation
Fetal
cells
Fetal
cells
Several
weeks
Figure 9.10 A
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Biochemical
tests
Karyotyping
Several
hours
Fetal Imaging
• Ultrasound imaging
– Uses sound waves to produce a picture of the fetus
Figure 9.10 B
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Newborn Screening
• Some genetic disorders can be detected at
birth
– By simple tests that are now routinely
performed in most hospitals in the United
States
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Ethical Considerations
• New technologies such as fetal imaging and
testing
– Raise new ethical questions
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VARIATIONS ON MENDEL’S LAWS
9.11 The relationship of genotype to phenotype is
rarely simple
• Mendel’s principles are valid for all sexually
reproducing species
– But genotype often does not dictate
phenotype in the simple way his laws
describe
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9.12 Incomplete dominance results in intermediate phenotypes
•
When an offspring’s phenotype is in between the phenotypes of its parents
– It exhibits incomplete dominance
P generation

Red
RR
Gametes
R
White
rr
r
F1 generation
Pink
Rr
Gametes 1 R
2
1
r
2
Sperm
1
1
r
R
2
2
F2 generation
Eggs
1
R
2
Red
RR
Pink
rR
1
r
2
Pink
Rr
White
rr
Figure 9.12 A
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Genotypes:
HH
Homozygous
for ability to make
LDL receptors
Hh
Heterozygous
hh
Homozygous
for inability to make
LDL receptors
Phenotypes:
LDL
LDL
receptor
Cell
Normal
Figure 9.12 B
Mild disease
Severe disease
9.13 Many genes have more than two alleles in
the population
• In a population
– Multiple alleles often exist for a
characteristic
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• The ABO blood type in humans
– Involves three alleles of a single gene
• The alleles for A and B blood types are codominant
– And both are expressed in the phenotype
Blood
Group
(Phenotype)
Genotypes
Antibodies
Present in
Blood
O
ii
Anti-A
Anti-B
A
IAIA
or
IAi
Anti-B
B
IBIB
or
IBi
Anti-A
AB
IAIB
—
Reaction When Blood from Groups Below Is Mixed with
Antibodies from Groups at Left
Figure 9.13
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O
A
B
AB
9.14 A single gene may affect many phenotypic
characteristics
• In pleiotropy
– A single gene may affect phenotype in many ways
Individual homozygous
for sickle-cell allele
Sickle-cell (abnormal) hemoglobin
Abnormal hemoglobin crystallizes,
causing red blood cells to become sickle-shaped
Sickle cells
Clumping of cells
and clogging of
small blood vessels
Breakdown of
red blood cells
Physical
weakness
Anemia
Impaired
mental
function
Heart
failure
Paralysis
Figure 9.14
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Pain and
fever
Pneumonia
and other
infections
Accumulation of
sickled cells in spleen
Brain
damage
Damage to
other organs
Rheumatism
Spleen
damage
Kidney
failure
9.15 A single characteristic may be influenced by many genes
• Polygenic inheritance
– Creates a continuum of phenotypes

P generation
aabbcc
(very light)
AABBCC
(very dark)

F1 generation
AaBbCc
AaBbCc
1
64
Sperm
1
8
1
8
1
8
1
8
1
8
1
8
1
8
1
8
1
8
1
Eggs 8
1
8
1
8
1
8
1
8
F2 generation
Figure 9.15
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1
8
1
8
6
64
15
64
20
64
20
64
15
64
6
64
1
64
Skin color
15
64
6
64
1
64
9.16 The environmental affects many
characteristics
• Many traits are affected, in varying degrees
– By both genetic and environmental factors
Figure 9.16
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CONNECTION
9.17 Genetic testing can detect disease-causing
alleles
• Predictive genetic testing
– May inform people of their risk for
developing genetic diseases
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THE CHROMOSOMAL BASIS OF INHERITANCE
9.18 Chromosome behavior accounts for
Mendel’s laws
• Genes are located on chromosomes
– Whose behavior during meiosis and
fertilization accounts for inheritance
patterns
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• The chromosomal basis of Mendel’s laws
All round yellow seeds
(RrYy)
F1 generation
R
r
y
Y
R
Y
R
r
Y
y
Metaphase I
of meiosis
(alternative arrangements)
r
R
Y
y
r
Anaphase I
of meiosis
y
r
R
r
R
Y
y
r
R
Y
y
Metaphase II
of meiosis
y
Y
Y
y
Y
Gametes
R
R
1
4
Y
y
r
1
4
RY
F2 generation
r
r
9
ry
r
1
4
rY
Fertilization among the F1 plants
:3
Figure 9.18
Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings
:3
:1
(See Figure 9.5A)
y
y
Y
R
R
1
4
Ry
9.19 Genes on the same chromosome tend to be
inherited together
Experiment
Purple flower
• Certain genes are linked
 PpLI
PpLI
– They tend to be inherited
together because they
reside close together on
the same chromosome
Observed
offspring
Phenotypes
Purple long
Purple round
Red long
Red round
Long pollen
Prediction
(9:3:3:1)
215
71
71
24
284
21
21
55
Explanation: linked genes
PL
Parental
diploid cell
PpLI
PI
Meiosis
Most
gametes
PL
PI
Fertilization
Sperm
Most
offspring
PL
PI
PL
PL
PL
PI
PI
PI
PL
PI
PL
Eggs
PI
3 purple long : 1 red round
Not accounted for: purple round and red long
Figure 9.19
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9.20 Crossing over produces new combinations
of alleles
• Crossing over can separate linked alleles
– Producing gametes with recombinant
chromosomes
A
B
a
b
A
b
a
B
A B
a
Tetrad
b
Crossing over
Figure 9.20 A
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Gametes
• Thomas Hunt Morgan
– Performed some of the early studies of
crossing over using the fruit fly Drosophila
melanogaster
Figure 9.20 B
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• Morgan’s experiments
– Demonstrated the role
of crossing over in
inheritance
Experiment
Black body,
vestigial
wings
Gray body,
long wings
(wild type)

GgLI
ggll
Male
Female
Offspring
Gray long
Black vestigial Gray vestigial Black long
965
944
206
Parental
phenotypes
Recombinant
phenotypes
Recombination frequency =
Explanation
391 recombinants
= 0.17 or 17%
2,300 total offspring
GL
g l
g l
gl
GgLI
(female)
GL
g l
Gl
gL
Eggs
GL
gl
gl
gl
Offspring
Figure 9.20 C
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185
Gl
gl
ggll
(male)
gl
Sperm
gL
gl
9.21 Geneticists use crossover data to map
genes
• Morgan and his students
– Used crossover data to map genes in
Drosophila
Figure 9.21 A
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• Recombination frequencies
– Can be used to map the relative positions
of genes on chromosomes.
Mutant phenotypes
Short
aristae
Chromosome
g
Black
body
(g)
Cinnabar
eyes
(c)
Vestigial
wings
(l)
Brown
eyes
Red
eyes
(C)
Normal
wings
(L)
Red
eyes
l
c
17%
9%
9.5%
Recombination
frequencies
Long aristae
(appendages
on head)
Gray
body
(G)
Wild-type phenotypes
Figure 9.21 B
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Figure 9.21 C
SEX CHROMOSOMES AND SEX-LINKED GENES
9.22 Chromosomes determine sex in many
species
• In mammals, a male has one X chromosome
and one Y chromosome
– And a female has two X chromosomes
(male)
44
Parents’
+
diploid
XY
cells
22
+
X
Figure 9.22 A
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(female)
44
+
XX
22
+
Y
Sperm
22
+
X
44
+
XX
44
+
XY
Offspring
(diploid)
Egg
• The Y chromosome
– Has genes for the development of testes
• The absence of a Y chromosome
– Allows ovaries to develop
Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings
• Other systems of sex determination exist in
other animals and plants
22
+
XX
22
+
X
76
+
ZW
76
+
ZZ
32
16
Figure 9.22 B
Figure 9.22 C
Figure 9.22 D
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9.23 Sex-linked genes exhibit a unique pattern of
inheritance
• All genes on the sex chromosomes
– Are said to be sex-linked
• In many organisms
– The X chromosome carries many genes
unrelated to sex
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• In Drosophila
– White eye color is a sex-linked trait
Figure 9.23 A
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• The inheritance pattern of sex-linked genes
– Is reflected in females and males
Female

XR XR
Male
Female
Xr Y
XR Xr

Eggs XR
Y
XR Xr
XR Y
Female
XR Y
XR X r
XR
Figure 9.23 B
Xr Y
Sperm
XR
Y
XR XR
XR Y
XR
Xr
Y
XR Xr
XR Y
Xr Xr
Xr Y
Eggs
Eggs
R = red-eye allele
r = white-eye allele
Male

Sperm
Sperm
Xr
Male
Xr
Xr XR
Figure 9.23 C
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Xr Y
Xr
Figure 9.23 D
CONNECTION
9.24 Sex-linked disorders affect mostly males
• Most sex-linked human disorders
– Are due to recessive alleles
– Are mostly seen in males
Queen
victoria
Albert
Alice
Louis
Alexandra
Figure 9.24 A
Figure 9.24 B
Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings
Czar
Nicholas II
of Russia
Alexis
• A male receiving a single X-linked allele from
his mother
– Will have the disorder
• A female
– Has to receive the allele from both parents
to be affected
Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings

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