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BIOLOGY
CONCEPTS & CONNECTIONS
Fourth Edition
Neil A. Campbell • Jane B. Reece • Lawrence G. Mitchell • Martha R. Taylor
CHAPTER 9
Patterns of Inheritance
Modules 9.11 – 9.23
From PowerPoint® Lectures for Biology: Concepts & Connections
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
VARIATIONS ON MENDEL’S PRINCIPLES
9.11 The relationship of genotype to phenotype is
rarely simple
• Mendel’s principles are valid for all sexually
reproducing species
– However, often the genotype does not dictate the
phenotype in the simple way his principles
describe
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9.12 Incomplete dominance results in intermediate
phenotypes
• When an offspring’s
phenotype—such
as flower color— is
in between the
phenotypes of its
parents, it exhibits
incomplete
dominance
P GENERATION
White
rr
Red
RR
Gametes
R
r
Pink
Rr
F1 GENERATION
1/
1/
Eggs
1/
F2 GENERATION
2
2
2
R
1/
2
r
1/
R
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R
Red
RR
r
Pink
Rr
Sperm
1/
Pink
rR
White
rr
Figure 9.12A
2
2
r
• Incomplete dominance in human
hypercholesterolemia
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
Mild disease
Figure 9.12B
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Severe disease
9.13 Many genes have more than two alleles in the
population
• In a population, multiple alleles often exist for a
characteristic
– The three alleles for ABO blood type in humans
is an example
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– 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
Reaction When Blood from Groups Below Is Mixed with
Antibodies from Groups at Left
O
O
ii
Anti-A
Anti-B
A
IA IA
or
IA i
Anti-B
B
IB IB
or
IB i
Anti-A
AB
IA IB
Figure 9.13
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A
B
AB
9.14 A single gene may affect many phenotypic
characteristics
• A single gene may affect phenotype in many
ways
– This is called pleiotropy
– The allele for sickle-cell disease is an example
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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
Impaired
mental
function
Anemia
Heart
failure
Pain and
fever
Paralysis
Brain
damage
Pneumonia
and other
infections
Accumulation of
sickled cells in spleen
Damage to
other organs
Rheumatism
Spleen
damage
Kidney
failure
Figure 9.14
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9.15 Connection: Genetic testing can detect
disease-causing alleles
• Genetic testing can be of
value to those at risk of
developing a genetic disorder
or of passing it on to offspring
Figure 9.15B
• Dr. David Satcher, former U.S.
surgeon general, pioneered
screening for sickle-cell disease
Figure 9.15A
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9.16 A single characteristic may be influenced by
many genes
• This situation creates a continuum of
phenotypes
– Example: skin color
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P GENERATION
aabbcc
AABBCC
(very light) (very dark)
F1 GENERATION
Eggs
Sperm
Fraction of population
AaBbCc AaBbCc
Skin pigmentation
F2 GENERATION
Figure 9.16
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THE CHROMOSOMAL BASIS OF
INHERITANCE
9.17 Chromosome behavior accounts for Mendel’s
principles
• Genes are located on chromosomes
– Their behavior during meiosis accounts for
inheritance patterns
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• The chromosomal basis of Mendel’s principles
Figure 9.17
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9.18 Genes on the same chromosome tend to be
inherited together
• Certain genes are linked
– They tend to be inherited together because they
reside close together on the same chromosome
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Figure 9.18
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9.19 Crossing over produces new combinations of
alleles
• This produces gametes with recombinant
chromosomes
• The fruit fly Drosophila melanogaster was used
in the first experiments to demonstrate the
effects of crossing over
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A
B
a
b
a
B
A B
a
b
Tetrad
A
b
Crossing over
Gametes
Figure 9.19A, B
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Figure 9.19C
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9.20 Geneticists use crossover data to map genes
• Crossing over is more likely to occur between
genes that are farther apart
– Recombination frequencies can be used to map
the relative positions of genes on chromosomes
Chromosome
g
c
l
17%
9%
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9.5%
Figure 9.20B
• Alfred H. Sturtevant, seen here at a party with
T. H. Morgan and his students, used
recombination data from Morgan’s fruit fly
crosses to map genes
Figure 9.20A
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• A partial genetic map of a fruit fly chromosome
Mutant phenotypes
Short
aristae
Black
body
(g)
Long aristae
(appendages
on head)
Gray
body
(G)
Cinnabar
eyes
(c)
Red
eyes
(C)
Vestigial
wings
(l)
Brown
eyes
Normal
wings
(L)
Red
eyes
Wild-type phenotypes
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Figure 9.20C
SEX CHROMOSOMES AND SEX-LINKED
GENES
9.21 Chromosomes determine sex in many species
• A human male has one X chromosome and one
Y chromosome
• A human female has two X chromosomes
• Whether a sperm cell has an X or Y
chromosome determines the sex of the
offspring
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(male)
(female)
Parents’
diploid
cells
X
Y
Male
Sperm
Egg
Offspring
(diploid)
Figure 9.21A
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• Other systems of sex determination exist in
other animals and plants
– The X-O system
– The Z-W system
– Chromosome number
Figure 9.21B-D
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9.22 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
– Fruit fly eye
color is a
sex-linked
characteristic
Figure 9.22A
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– Their inheritance pattern reflects the fact that
males have one X chromosome and females
have two
– These figures illustrate inheritance patterns for
white eye color (r) in the fruit fly, an X-linked
recessive trait
Female
XRXR
Male
Xr Y
XR
Female
XRXr
Xr
XRXr
Male
XRY
XRY
Xr
XRXR
XrXR
XRY
XrY
R = red-eye allele
r = white-eye allele
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Male
XRXr
XR
XR
Y
Female
XrY
Xr
XR
Y
Xr
XRXr
Xr Xr
Y
XRY
XrY
Figure 9.22B-D
9.23 Connection: Sex-linked disorders affect
mostly males
• Most sex-linked human
disorders are due to
recessive alleles
– Examples: hemophilia,
red-green color blindness
– These are mostly seen in males
Figure 9.23A
– A male receives a single X-linked allele from his
mother, and will have the disorder, while a
female has to receive the allele from both
parents to be affected
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• A high incidence of hemophilia has plagued the
royal families of Europe
Queen
Victoria
Albert
Alice
Louis
Alexandra
Czar
Nicholas II
of Russia
Alexis
Figure 9.23B
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings