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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 9.1 – 9.10
From PowerPoint® Lectures for Biology: Concepts & Connections
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
MENDEL’S PRINCIPLES
9.1 The science of genetics has ancient roots
• Science of heredity dates back to ancient
attempts at selective breeding
• Until the 20th century, however, many
biologists erroneously believed that
– characteristics acquired during lifetime could be
passed on
– characteristics of both parents blended
irreversibly in their offspring
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
9.2 Experimental genetics began in an abbey
garden
• Modern genetics began with Gregor Mendel’s
quantitative experiments with pea plants
Stamen
Carpel
Figure 9.2A, B
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• Mendel self and
cross fertilized
plants
White
1
Removed
stamens
from purple
flower
Stamens
Carpel
PARENTS
(P)
2 Transferred
Purple
pollen from
stamens of white
flower to carpel
of purple flower
3 Pollinated carpel
matured into pod
• This illustration
shows his
technique for
cross-fertilization
4
OFFSPRING
(F1)
Figure 9.2C
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Planted
seeds
from pod
• Mendel studied 7
pea characteristics
FLOWER
COLOR
Purple
White
Axial
Terminal
SEED
COLOR
Yellow
Green
SEED
SHAPE
Round
Wrinkled
POD
SHAPE
Inflated
Constricted
POD
COLOR
Green
Yellow
STEM
LENGTH
Tall
Dwarf
FLOWER
POSITION
• Hypothesized
alleles
Figure 9.2D
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9.3 Mendel’s principle of segregation describes the
inheritance of a single characteristic
• From his
experimental data,
Mendel deduced
that an organism
has 2(alleles) for
each inherited
characteristic
P GENERATION
(true-breeding
parents)
Purple flowers
White flowers
All plants have
purple flowers
F1
generation
Fertilization
among F1
plants
(F1 x F1)
– 1 characteristic
from each parent
F2
generation
Figure 9.3A
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3/
of plants
have purple flowers
4
1/
4 of plants
have white flowers
• A sperm or egg
carries only 1 allele
of each pair
– The pairs of alleles
separate when
gametes form
GENETIC MAKEUP (ALLELES)
P PLANTS
Gametes
PP
pp
All P
All p
F1 PLANTS
(hybrids)
Gametes
– This process
describes Mendel’s
law of segregation
All Pp
1/
2
1/
P
P
2
p
P
Eggs
Sperm
PP
F2 PLANTS
– Alleles can be
dominant or
recessive
Phenotypic ratio
3 purple : 1 white
p
p
Pp
Pp
pp
Genotypic ratio
1 PP : 2 Pp : 1 pp
Figure 9.3B
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9.4 Homologous chromosomes bear the two alleles
for each characteristic
• Alternative forms of a gene (alleles) reside at
the same locus on homologous chromosomes
GENE LOCI
P
P
a
a
B
DOMINANT
allele
b
RECESSIVE
allele
GENOTYPE:
PP
aa
HOMOZYGOUS
for the
dominant allele
HOMOZYGOUS
for the
recessive allele
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Bb
HETEROZYGOUS
Figure 9.4
• Independent assortment of two genes in the
Labrador retriever
Blind
PHENOTYPES
GENOTYPES
Black coat,
normal vision
B_N_
Black coat,
blind (PRA)
B_nn
MATING OF HETEROZYOTES
(black, normal vision)
PHENOTYPIC RATIO
OF OFFSPRING
9 black coat,
normal vision
BbNn
3 black coat,
blind (PRA)
Figure 9.5B
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Blind
Chocolate coat,
normal vision
bbN_
Chocolate coat,
blind (PRA)
bbnn
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 often reveal the
genotype of an individual when it is unknown
TESTCROSS:
GENOTYPES
B_
bb
Two possibilities for the black dog:
BB
b
OFFSPRING
Bb
B
GAMETES
Figure 9.6
or
Bb
All black
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B
b
Bb
b
bb
1 black : 1 chocolate
9.8 Connection: Genetic traits in humans can be
tracked through family pedigrees
• The inheritance of many
human traits follows
Mendel’s principles and
the rules of probability
Figure 9.8A
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• Family pedigrees are used to determine
patterns of inheritance and individual
genotypes
Dd
Joshua
Lambert
Dd
Abigail
Linnell
D_?
Abigail
Lambert
D_?
John
Eddy
dd
Jonathan
Lambert
Dd
Dd
dd
D_?
Hepzibah
Daggett
Dd
Elizabeth
Eddy
Dd
Dd
Dd
dd
Female Male
Deaf
Figure 9.8B
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Hearing
9.9 Connection: Many inherited disorders in
humans are controlled by a single gene
• Most such
disorders are
caused by
autosomal
recessive alleles
– Examples:
cystic fibrosis,
sickle-cell
disease
Normal
Dd
PARENTS
Normal
Dd
D
D
Eggs
Sperm
DD
Normal
d
OFFSPRING
d
Dd
Normal
(carrier)
Dd
Normal
(carrier)
dd
Deaf
Figure 9.9A
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9.12 Incomplete dominance results in intermediate
phenotypes
• Incomplete
dominance:
phenotype blend
because alleles
“blend”, but not
irreversible
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 Multiple Alleles
• Blood type example of multiple alleles
– The three alleles for ABO blood type in humans
is an example:
- IA, IB, i
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– Alleles A and B CODOMINANT
– 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
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
– Tend to be passed down together because close
together on same chromosome
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Figure 9.18
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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
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
• Sex-linked genes: genes on the sex
chromosomes
– 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
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