Transcript Document

Chapter 9
Patterns of Inheritance
PowerPoint® Lectures for
Campbell Essential Biology, Fifth Edition, and
Campbell Essential Biology with Physiology,
Fourth Edition
– Eric J. Simon, Jean L. Dickey, and Jane B. Reece
Lectures by Edward J. Zalisko
© 2013 Pearson Education, Inc.
Biology and Society:
Our Longest-Running Genetic Experiment: Dogs
• 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.
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Figure 9.0
HERITABLE VARIATION AND PATTERNS
OF INHERITANCE
• 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.
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Figure 9.1
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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Figure 9.2
Petal
Stamen
(makes spermproducing
pollen)
Carpel
(produces eggs)
Figure 9.3-1
1 Removed
stamens
from purple
flower.
Stamens
Parents
(P)
Carpel
2 Transferred pollen from
stamens of white flower
to carpel of purple flower.
Figure 9.3-2
1 Removed
stamens
from purple
flower.
Stamens
Parents
(P)
Carpel
2 Transferred pollen from
stamens of white flower
to carpel of purple flower.
3 Pollinated carpel
matured into pod.
Figure 9.3-3
1 Removed
stamens
from purple
flower.
Stamens
Parents
(P)
Carpel
2 Transferred pollen from
stamens of white flower
to carpel of purple flower.
3 Pollinated carpel
matured into pod.
4 Planted seeds
from pod.
Offspring
(F1)
In an Abbey Garden
• 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.
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In an Abbey Garden
• Mendel
– created purebred varieties of plants and
– crossed two different purebred varieties.
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In an Abbey Garden
• 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.
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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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Figure 9.4
Dominant
Dominant
Recessive
Pod
shape
Flower
color
Inflated
Purple
White
Flower
position
Seed
color
Seed
shape
Recessive
Axial
Terminal
Yellow
Green
Round
Wrinkled
Constricted
Pod
color
Green
Yellow
Tall
Dwarf
Stem
length
Figure 9.4a
Monohybrid 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
P Generation
(purebred
parents)
Purple
flowers
White
flowers
Figure 9.5-2
P Generation
(purebred
parents)
Purple
flowers
F1 Generation
White
flowers
All plants have
purple flowers
Figure 9.5-3
P Generation
(purebred
parents)
Purple
flowers
White
flowers
F1 Generation
All plants have
purple flowers
Fertilization
among F1 plants
(F1  F1)
F2 Generation
3
4 of plants
have purple flowers
1
4 of plants
have white flowers
Figure 9.5a
Monohybrid Crosses
• 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.
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Monohybrid Crosses
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.
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Monohybrid Crosses
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.
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Monohybrid Crosses
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.
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Monohybrid Crosses
• 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.
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Figure 9.6
P Generation
Genetic makeup (alleles)
Purple flowers
Alleles carried
PP
by parents
Gametes
White flowers
pp
All p
All P
F1 Generation
(hybrids)
Purple flowers
All Pp
Alleles
segregate
Gametes
1
P
2
F2 Generation
(hybrids)
1 p
2
Sperm from
F1 plant
P
p
PP
Pp
Pp
pp
P
Eggs from
F1 plant
p
Phenotypic ratio Genotypic ratio
3 purple : 1 white 1 PP : 2 Pp : 1 pp
Monohybrid Crosses
• 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.
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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
Homologous
chromosomes
Gene loci
Genotype:
Dominant
allele
P
a
B
P
a
b
PP
Homozygous
for the
dominant allele
aa
Homozygous
for the
recessive allele
Recessive
allele
Bb
Heterozygous
with one dominant
and one recessive
allele
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.
© 2013 Pearson Education, Inc.
Figure 9.8b
Sperm
1
4
1
4
RY
1
4
rY
RY
1
4
rY
1
4
Ry
1
4
ry
RRYY RrYY RRYy RrYy
RrYY rrYY RrYy rrYy
Eggs
1
4
Ry
1
4
ry
F2 Generation
9
16
Yellow
round
RRYy RrYy RRyy Rryy
3
16
Green
round
RrYy rrYy Rryy
3
16
Yellow
wrinkled
1
16
Green
wrinkled
rryy
Actual results
(support hypothesis)
Figure 9.8c
Mendel’s Law of Independent Assortment
• 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.
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Figure 9.9
Blind dog
Blind dog
Phenotypes
Genotypes
Black coat,
normal vision
B_N_
Black coat,
blind (PRA)
B_nn
Chocolate coat,
normal vision
bbN_
Chocolate coat,
blind (PRA)
bbnn
(a) Possible phenotypes of Labrador retrievers
Mating of double
heterozygotes
(black coat, normal vision)
BbNn
BbNn
Blind
Phenotypic
ratio of
offspring
9 black coat,
normal vision
(b) A Labrador dihybrid cross
3 black coat,
blind (PRA)
Blind
3 chocolate coat,
normal vision
1 chocolate coat,
blind (PRA)
Figure 9.9a
Mating of double hererozygotes
(BbNn  BbNn)
Blind
9 black coat,
normal vision
3 black coat,
blind (PRA)
Blind
3 chocolate coat,
normal vision
1 chocolate coat,
blind (PRA)
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
Testcross
Genotypes
bb
B_
Two possible genotypes for the black dog:
BB
Gametes
B
b
Offspring
Bb
or
Bb
All black
b
B
b
Bb
bb
1 black : 1 chocolate
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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F1 Genotypes
Bb female
Bb male
Formation of eggs
Formation of sperm
F2 Genotypes
Male
gametes
1
2
Female gametes
Figure 9.11
1
2
B
B
B
B
1
2
b
B
1
4
1
4
( 1  1)
2
1
2
b
b
2
b
B
1
4
b
b
1
4
Family Pedigrees
• Mendel’s principles apply to the inheritance of
many human traits.
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DOMINANT TRAITS
Figure 9.12
Widow’s peak
Free earlobe
No freckles
Straight hairline
Attached earlobe
RECESSIVE TRAITS
Freckles
Family Pedigrees
• 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.
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Family Pedigrees
• A family pedigree
– shows the history of a trait in a family and
– allows geneticists to analyze human traits.
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Figure 9.13
First generation
(grandparents)
Second generation
(parents, aunts, and
uncles)
Third generation
(brother and
sister)
Aaron
Ff
Betty
Ff
Evelyn Fred Gabe Hal
FF
ff
ff
Ff
or
Ff
Kevin
ff
Female Male
Attached
Female Male
Free
Cletus
ff
Ina
Ff
Lisa
FF
or
Ff
Debra
Ff
Jill
ff
Figure 9.13a
Figure 9.13b
Figure 9.13c
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
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
Hearing
Dd
Hearing
Dd
Offspring
D Sperm d
D
DD
Hearing
Dd
Hearing
(carrier)
Dd
Hearing
(carrier)
dd
Deaf
Eggs
d
Recessive Disorders
• 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.
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Recessive Disorders
• 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.
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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
Figure 9.16
Parents
Normal
(no achondroplasia)
dd
Dwarf
(achondroplasia)
Dd
d Sperm
D
d
Dd
Dwarf
Dd
Dwarf
dd
Normal
dd
Normal
Eggs
d
Jeremy
Molly Jo
Jacob
Zachary
Matt
Amy
The Process of Science:
What Is the Genetic Basis of Coat Variation in Dogs?
• Observation: Dogs come in a wide variety of physical
types.
• Question: What is the genetic basis for canine coats?
• Hypothesis: A comparison of genes of a wide variety
of dogs with different coats would identify the genes
responsible.
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The Process of Science:
What Is the Genetic Basis of Coat Variation in Dogs?
• Prediction: Mutations in just a few genes account for
the coat appearance.
• Experiment: Compared DNA sequences of 622 dogs
from dozens of breeds.
• Results: Three genes in different combinations
produced seven different coat appearances, from very
short hair to full, thick, wired hair.
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Figure 9.17
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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VARIATIONS ON MENDEL’S LAWS
• Some patterns of genetic inheritance are not
explained by Mendel’s laws.
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Incomplete Dominance in Plants and People
• In incomplete dominance, F1 hybrids have an
appearance between the phenotypes of the two
parents.
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Figure 9.18-1
P Generation
White
rr
Red
RR
Gametes
R
r
Figure 9.18-2
P Generation
White
rr
Red
RR
Gametes
r
R
F1 Generation
Pink
Rr
Gametes
1
2
R
1
2
r
Figure 9.18-3
P Generation
White
rr
Red
RR
Gametes
r
R
F1 Generation
Pink
Rr
Gametes
1
2
R
F2 Generation
1
2
r
Sperm
1
2
1
2
R
Eggs
1
2
R
1
2
r
RR
Rr
Rr
rr
r
Incomplete Dominance in Plants and People
• Hypercholesterolemia
– is a human trait that is an example of incomplete
dominance and
– is characterized by dangerously high levels of
cholesterol in the blood.
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Incomplete Dominance in Plants and People
• In hypercholesterolemia,
– heterozygotes have blood cholesterol levels about
twice normal, and
– homozygotes have about five times the normal
amount of blood cholesterol and may have heart
attacks as early as age 2.
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GENOTYPE
Figure 9.19
HH
Homozygous
for ability to make
LDL receptors
Hh
Heterozygous
hh
Homozygous
for inability to make
LDL receptors
Mild disease
Severe disease
PHENOTYPE
LDL
LDL
receptor
Cell
Normal
ABO Blood Groups: An Example of Multiple
Alleles and Codominance
• The ABO blood groups in humans are an
example of multiple alleles.
• The immune system produces blood proteins
called antibodies that bind specifically to foreign
carbohydrates.
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ABO Blood Groups: An Example of Multiple
Alleles and Codominance
• If a donor’s blood cells have a carbohydrate (A or
B) that is foreign to the recipient, the blood cells
may clump together, potentially killing the recipient.
• The clumping reaction is the basis of a bloodtyping lab test.
• The human blood type alleles IA and IB are
codominant, meaning that both alleles are
expressed in heterozygous individuals who have
type AB blood.
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Figure 9.20
Blood
Group
(Phenotype) Genotypes
Red Blood Cells
Carbohydrate
A
Antibodies
Present in
Blood
A
IAIA
or
IAi
B
IBIB
or
IBi
AB
IAIB
—
O
ii
Anti-A
Anti-B
Carbohydrate
B
Anti-B
Anti-A
Reactions When Blood from Groups Below
Is Mixed with Antibodies from Groups at Left
A
O
B
AB
Figure 9.20c
Pleiotropy and Sickle-Cell Disease
• Pleiotropy is when one gene influences several
characters.
• Sickle-cell disease
– exhibits pleiotropy,
– results in abnormal hemoglobin proteins, and
– causes disk-shaped red blood cells to deform into
a sickle shape with jagged edges.
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Figure 9.21
Individual homozygous
for sickle-cell allele
Sickle-cell (abnormal) hemoglobin
Colorized SEM
Abnormal hemoglobin crystallizes
into long flexible chains, causing
red blood cells to become
sickle-shaped.
Sickled cells can lead to a cascade
of symptoms, such as weakness,
pain, organ damage, and paralysis.
Figure 9.21a
Polygenic Inheritance
• Polygenic inheritance is the additive effects of
two or more genes on a single phenotype.
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Figure 9.22
 short allele
 tall allele
P Generation
aabbcc
(very short)
AABBCC
(very tall)
F1 Generation
AaBbCc
(medium height)
Sperm
F2 Generation
1
8
AaBbCc
(medium height)
1
8
1
8
1
8
1
8
1
8
1
8
1
8
20
64
Fraction of population
1
8
1
8
Eggs
1
8
1
8
1
8
1
8
1
8
1
8
15
64
6
64
1
64
Very short
1
64
6
64
15
64
20
64
15
64
6
64
1
64
Adult height
Very tall
Figure 9.22a
 short allele
 tall allele
P Generation
aabbcc
(very short)
AABBCC
(very tall)
F1 Generation
AaBbCc
(medium height)
AaBbCc
(medium height)
Figure 9.22b
F2 Generation
1
8
1
8
1
8
1
8
1
8
1
8
1
8
1
8
1
8
1
8
1
8
1
8
1
8
1
8
1
8
1
8
 short allele
 tall allele
1
64
6
64
15
64
20
64
15
64
6
64
1
64
Figure 9.22c
Fraction of population
20
64
15
64
6
64
1
64
Very short
Adult height
Very tall
The Role of Environment
• Many human characters result from a combination
of
– heredity and
– environment.
• Only genetic influences are inherited.
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Figure 9.23
THE CHROMOSOMAL BASIS OF
INHERITANCE
• The chromosome theory of inheritance states
that
– genes are located at specific positions (loci) on
chromosomes and
– the behavior of chromosomes during meiosis and
fertilization accounts for inheritance patterns.
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THE CHROMOSOMAL BASIS OF
INHERITANCE
• It is chromosomes that
– undergo segregation and independent assortment
during meiosis and
– account for Mendel’s laws.
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Figure 9.24
P Generation
Round-yellow
seeds
(RRYY)
r y
Y
Y
Wrinkled-green
seeds
(rryy)
R R
r
y
MEIOSIS
FERTILIZATION
Gametes
y
R Y
F1 Generation
All round-yellow
seeds
(RrYy)
R
R
Y
The R and r alleles segregate in
anaphase I of meiosis.
Y
r
MEIOSIS
r
R
y
Metaphase I
(alternative
arrangements)
Y
y
r
R
Only one long
chromosome ends
up in each gamete.
Gametes
y
Y
R
1
4
Metaphase
II
r
1
4
Y
y
Y
r
1
4
rY
FERTILIZATION AMONG THE F1 PLANTS
9
: 3
: 3
They are arranged in either of
two equally likely ways at
metaphase I.
R
r
ry
Law of Independent Assortment:
Follow both the long and the short
chromosomes.
r
Y
y
r
RY
Fertilization recombines the r
and R alleles at random.
F2 Generation
y
Y
Y
R
y
r
Law of Segregation: Follow the long
chromosomes (carrying R and r) taking
either the left or right branch.
r
:1
They sort independently,
giving four gamete types.
y
y
R
R
1
4
Ry
Fertilization results in the 9:3:3:1
phenotypic ratio in the F2 generation.
Figure 9.24a
F1 Generation
All round-yellow
seeds
(RrYy)
Law of Independent
Assortment: Follow
both the long and the
short chromosomes.
R
Law of Segregation:
Follow the long
chromosomes.
Y
The R and r alleles
segregate in
anaphase I.
R
Only one long
chromosome
ends up
Y
in each
gamete.
R
r
r
R
Y
y
Y
y
Y
R
1
4
RY
Fertilization recombines
the r and R alleles at
random.
r
R
y
Y
y
Y
y
r
r
1
4
They are arranged in
either of two equally
likely ways at
metaphase I.
r
y
Y
R
y
r
ry
r
1
4
rY
y
y
Y
r
They sort
independently,
giving four
gamete types.
R
R
1
4
Ry
Fertilization results in the
9:3:3:1 phenotypic ratio in
the F2 generation.
Linked Genes
• Linked genes
– are located close together on a chromosome and
– tend to be inherited together.
• Thomas Hunt Morgan
– used the fruit fly Drosophila melanogaster and
– determined that some genes were linked based on
the inheritance patterns of their traits.
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Figure 9.25-1
Dihybrid testcross
Gray body,
long wings
(wild-type)
Black body,
short wings
(mutant)
GgLl
ggll
Female
Male
Figure 9.25-2
Dihybrid testcross
Gray body,
long wings
(wild-type)
Black body,
short wings
(mutant)
GgLl
ggll
Female
Male
Results
Offspring
Gray-long
GgLl
965
Black-short
ggll
944
Parental phenotypes 83%
Gray-short
Ggll
206
Black-long
ggLl
185
Recombinant phenotypes 17%
Genetic Recombination: Crossing Over
• Crossing over can
– separate linked alleles,
– produce gametes with recombinant gametes, and
– produce offspring with recombinant phenotypes.
• The percentage of recombinant offspring among
the total is called the recombination frequency.
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Figure 9.26
A B
a b
A B
Parental gametes
a b
Pair of
homologous
chromosomes
Crossing over
A b
a B
Recombinant gametes
Figure 9.27
GgLl
(female)
GL
gl
gl
gl
ggll
(male)
CROSSING OVER
gl
GL
Gl
gL
gl
Sperm
Parental gametes Recombinant gametes
Eggs
FERTILIZATION
Offspring
GL
gl
Gl
gL
gl
gl
gl
gl
Parental
Recombinant
Linkage Maps
• Early studies of crossing over were performed
using the fruit fly Drosophila melanogaster.
• Alfred H. Sturtevant, a student of Morgan,
– developed a method for mapping the relative gene
locations,
– which resulted in the creation of linkage maps.
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Figure 9.28
Chromosome
g
c
l
17%
9%
9.5%
Recombination
frequencies
SEX CHROMOSOMES AND SEX-LINKED
GENES
• Sex chromosomes influence the inheritance of
certain traits. For example, humans that have a
pair of sex chromosomes designated
– X and Y are male or
– X and X are female.
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Figure 9.29a
Male
44

XY
22

X
Female
44
Somatic

cells
XX
22

Y
Sperm
44

XX
22

X
Egg
Offspring
Female
44

XY
Male
Figure 9.29b
X
Colorized SEM
Y
Sex Determination in Humans
• Nearly all mammals have a pair of sex
chromosomes designated X and Y.
– Males have an X and Y.
– Females have XX.
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Sex-Linked Genes
• Any gene located on a sex chromosome is called a
sex-linked gene.
– Most sex-linked genes are found on the X
chromosome.
– Red-green colorblindness is
– a common human sex-linked disorder and
– caused by a malfunction of light-sensitive cells in
the eyes.
© 2013 Pearson Education, Inc.
Figure 9.30
Figure 9.31
XNXN
Xn
X nY
Y
XNXn
XN
Sperm
Eggs XN
XNXn XNY
Eggs XN
XN
XNXn XNY
Xn
(a) Normal female  colorblind male
XNY
Y
XNXn
Carrier
X nY
(b) Carrier female  normal male
Colorblind individual
Xn
Sperm
XNXN XNY
Key
Unaffected individual
XNXn
Eggs XN
Xn
X nY
Y
Sperm
XNXn XNY
X nX n
X nY
(c) Carrier female  colorblind male
Figure 9.31a
XNXN
XnY
Key
Unaffected
individual
Xn
Y
Sperm
Carrier
Colorblind
individual
Eggs XN
XNXn XNY
XN
XNXn XNY
(a) Normal female  colorblind male
Figure 9.31b
XNXn
XNY
Key
Unaffected
individual
XN
Y
Sperm
Carrier
Colorblind
individual
Eggs XN
XNXN XNY
Xn
XNXn XnY
(b) Carrier female  normal male
Figure 9.31c
XNXn
XnY
Key
Unaffected
individual
Xn
Y
Sperm
Carrier
Colorblind
individual
Eggs XN
Xn
XNXn XNY
XnXn
XnY
(c) Carrier female  colorblind male
Sex-Linked Genes
• Hemophilia
– is a sex-linked recessive blood-clotting trait that
may result in excessive bleeding and death after
relatively minor cuts and bruises and
– has plagued the royal families of Europe.
© 2013 Pearson Education, Inc.
Figure 9.32
Albert
Queen
Victoria
Alice
Louis
Alexandra
Czar
Nicholas II
of Russia
Alexis
Evolution Connection:
Barking Up the Evolutionary Tree
• About 15,000 years ago in East Asia, people
began to cohabit with ancestral canines that were
predecessors of modern wolves and dogs.
• As people settled into geographically distinct
populations,
– different canines became separated and
– eventually became inbred.
© 2013 Pearson Education, Inc.
Evolution Connection:
Barking Up the Evolutionary Tree
• A 2010 study indicated that small dogs were
developed within the first permanent agricultural
settlements of the Middle East around 12,000
years ago.
• Continued over millennia, genetic tinkering has
resulted in a diverse array of dog body types and
behaviors.
© 2013 Pearson Education, Inc.
Figure 9.33
Wolf
Ancestral
canine
Chinese
shar-pei
Akita
Basenji
Siberian
husky
Alaskan
malamute
Afghan hound
Saluki
Rottweiler
Sheepdog
Retriever
Figure 9.33a
Figure 9.UN08