Transcript 10.6 Gene Expression Can Appear to Alter - OCC

10.6 Gene Expression Can Appear to Alter
Mendelian Ratios
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A. Incomplete Dominance andParental
generation
Codominance Add
Phenotype Classes
• Incomplete dominance
rr
×
r2r2
White flowers
1 1
Red flowers
– Heterozygote has
F generation
intermediate phenotype
– Crossing of 2 pink
snapdragons yields red, white
or pink offspring
3rd
1
r1r2
All pink flowers
Figure 10.14 Incomplete Dominance.
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Female gametes
Male gametes
F2 generation
r2
r1
r1
r1r1
r1r2
r1r2
r2r2
Red (r1r1) : 25% chance
Pink (r1r2) : 50% chance
White (r2r2) : 25% chance
r2
Figure 10.14 Incomplete Dominance.
10.6 Gene Expression Can Appear to Alter
Mendelian Ratios
A. Incomplete Dominance and Codominance
Add Phenotype Classes
• Codominance
– 2 different alleles expressed together
– Human ABO blood type
•
•
I gene – IA, IB, I – 3 alelles
A and B are codominant
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Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Genotypes
Phenotypes
Surface molecules
IAIA
IAi
Only A
ABO blood type
Type A
A
A
A
A
A
A
B
IBIB
IBi
Only B
B
B
B
B
Type B
B
IAIB
Both A and B
A
B
B
A
A
Type AB
B
ii
None
Type O
Figure 10.15 Codominance.
Clicker Question
• A woman who has type O blood has a son
with type O blood. Who below CANNOT be
the father?
A.A man with type A blood
B.A man with type O blood
C.A man with type AB blood
D.A man with type B blood
10.6 Gene Expression Can Appear to Alter
Mendelian Ratios
B. Some Inheritance Patterns Are Especially
Difficult to Interpret
• Pleiotropy
– One gene has multiple effect on the phenotype
– One protein important in different pathways or
tissues
– Marfan syndrome
– Porphyria variegata
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Porphyrin accumulates in the...
Urine
Digestive
system
Nervous
tissue
Muscles
Resulting in...
Delirium
Stupor
Constipation
Rapid pulse
Abdominal
pain
Darkcolored
urine
Weak limbs
Convulsions
Figure 10.16 Pleiotropy.
Mad
behavior
10.6 Gene Expression Can Appear to Alter
Mendelian Ratios
B. Some Inheritance Patterns Are Especially
Difficult to Interpret
• Protein interactions
– Can cause same phenotype from different
mutations
– Epistasis- one gene’s product affects the
expression of another gene
•
•
ABO blood type inconsistencies
Paternity confusions
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Genotypes
ABO Gene
Phenotypes
H Gene
IAIA
encodes
HH or Hh
encodes
A
A
A
A
A
Type A
Molecule A
Molecule H
A
attaches
to
IAIA
encodes
hh
mutant
Molecule A
cannot
attach
Molecule H
absent
Type O
Figure 10.17 Epistasis.
10.6 Mastering Concepts
Compare and contrast dominant,
recessive, incomplete dominant, and
codominant
10.7 Sex-Linked Genes Have Unique Inheritance
Patterns
• Huntington Disease, cystic fibrosis and others
from genes found on autosomes
– Affect both sexes equally
• Red-green color blindness, hemophilia genes
are found on sex chromosomes
– Affect one sex more than another
– Called sex-linked
10.7 Sex-Linked Genes Have Unique Inheritance
Patterns
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A. X and Y
Chromosomes
Determine Sex
in Humans
• Females XX
• Males XY
X
X
SEM (false color) 2 µm
Male gametes
Female gametes
X
X
X
X
XX
Girl
XX
Girl
XY
Boy
XY
Boy
Y
SEM (false color) 2 µm
Girl (XX) : 50% chance
Boy (XY) : 50% chance
© Andrew Syred/Photo Researchers
Figure 10.18 The Sperm Determines the Sex of the Baby.
10.7 Sex-Linked Genes Have Unique Inheritance
Patterns
A. X and Y Chromosomes Determine Sex in
Humans
• Y chromosome plays largest role in sex
determination
– SRY gene
– Few Y-linked disorders
• X-linked traits more common
10.7 Sex-Linked Genes Have Unique Inheritance
Patterns
B. X-Linked Recessive Disorders Affect More
Males Than Females
• Thomas Hunt Morgan and fruit flies
• Male white-eyed flies
– Gene must be on X chromosome
– Sex of parent mattered in crosses
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a. Cross of true breeding white-eyed male with red-eyed female
b. Cross of true breeding red-eyed male with white-eyed female
W
Dominant allele; encodes red eyes
W
Dominant allele; encodes red eyes
w
Recessive allele; encodes white eyes
w
Recessive allele; encodes white eyes
Female with red eyes
XW
XW
Xw
XW X w
XW Xw
Y
XW Y
XW Y
Female with white eyes
P
Male with white eyes
Male with white eyes
P
XW
Y
All off spring
Have red eyes
Female with red eyes
XW
Xw
XW
XW XW
XW Xw
Y
XW Y
Xw Y
Xw
XW Xw
XW X w
Xw Y
Xw Y
All females have red eyes
All males have white eyes
F1
Male with white eyes
Male with white eyes
F1
Xw
All females have red eyes
50% of males have red eyes
50% of males have white eyes
Figure 10.19 Fly Eyes.
Female with red eyes
XW
Xw
Xw
XW X w
Xw Xw
Y
XW Y
Xw Y
50% of females have red eyes
50% of females have white eyes
50% of males have red eyes
50% of males have white eyes
10.7 Sex-Linked Genes Have Unique Inheritance
Patterns
B. X-Linked Recessive Disorders Affect More
Males Than Females
• Female shows recessive X-linked trait only if
she inherits 2 recessive alleles
• Male expresses whatever is on his only X
• Hemophilia A
– X-linked recessive inheritance
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Mother: heterozygous
Female gametes
Male gametes
Father: healthy
XH
XH
Y
XHXH
Healthy
daughter
XHY
Healthy
son
Xh
XHXh
Healthy
daughter
(carrier)
XhY
Son with
hemophilia
Healthy daughter, noncarrier (XHXH): 25% chance
Healthy daughter, carrier (XHXh): 25% chance
Healthy son (XHY): 25% chance
Affected son (XhY): 25% chance
Figure 10.20 Hemophilia A.
10.7 Sex-Linked Genes Have Unique Inheritance
Patterns
C. X Inactivation Prevents “Double Dosing” of
Proteins
• Males have a “double dose” of every gene on
X
• Female cells shut off one X
– Barr body
– Random which X shut down
– Calico and tortoiseshell cats are always female
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Black
inactivation
X
Orange
inactivation
X
a.
Figure 10.21
X Inactivation.
b.
a: © William E. Ferguson; b: © Horst Schaefer/Peter Arnold/Photolibrary
10.7 Mastering Concepts
Why do males and females express
recessive X-linked alleles differently?
10.8 Pedigrees Show Modes of
Inheritance
• Genes on autosomes exhibit
– Autosomal dominant
•
Appears in every generation
– Autosomal recessive
•
•
May seem to skip generations
Carriers have normal phenotype
• X-linked conditions have unique patterns
• Pedigrees can be useful
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
a. Achondroplasia (autosomal dominant)
b. Albinism (autosomal recessive)
I
c. Red-green color blindness
(X-linked recessive)
I
1
I
1
2
II
2
3
4
II
1
2
3
4
5
6
7
8
III
2
3
Normal
4
5
2
II
1
2
3
III
1
1
4
1
5
2
3
4
5
6
III
1
2
3
1
2
3
4
Carrier Affected
Female
Male
a: © Rick Wilking/Reuters/Corbis; b: © Reuters/STRINGER Brazil; c: © BSIP/Photo Researchers
Figure 10.22 Pedigrees Reveal Mode of Inheritance.
5
Clicker Question
• In determining the inheritance mode of a
disorder, which factors below can cause
problems?
A.Humans typically have only a few children
B.Codominance or incomplete dominance
C.Protein interactions or epistasis
D.All of the above
10.9 Most Traits Are Influenced by the
Environments and Multiple Genes
A. The Environment Can Alter the Phenotype
• A gene may be active in one circumstance but
inactive in another
• Temperature in Siamese cats
• Fetal alcohol syndrome –
exposure to alcohol alters
phenotype
10.9 Most Traits Are Influenced by the
Environments and Multiple Genes
B. Polygenic Traits Depend on More Than One
Gene
• Phenotype reflects the activities of more than
one gene
– Eye color
– Male pattern baldness
• Bell-shaped curve or continuum of gene
expression
10.9 Most Traits Are Influenced by the
Environments and Multiple Genes
B. Polygenic Traits Depend on More Than One
Gene
• Bell-shaped curve or continuum of gene
expression
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4’10”
a.
5’0”
5’2”
5’4”
5’6”
5’8”
5’10”
6’0”
6’2”
5’0”
5’2”
5’4”
5’6”
5’8”
5’10”
b.
a–b: © Peter Morenus/University of Connecticut
Figure 10.24 Height Is Polygenic and Environmental.
6’0”
6’2”
6’4”
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Parent phenotypes:
medium tone
= Unit of pigment
×
Parent genotypes:
Possible
phenotypes
of children
AaBbCc
Light
Dark
6/64
1/64
aabbcc
Possible
genotypes
of children
AaBbCc
Aabbcc
aaBbcc
aabbCc
15/64
AaBbcc
AabbCc
AAbbcc
aaBBcc
aabbCC
aaBbCc
20/64
AaBbCc
aaBbCC
AAbbCc
AabbCC
AABbcc
aaBBCc
AaBBcc
15/64
aaBBCC
AAbbCC
AABBcc
AaBbCC
AaBBCc
AABbCc
© Sarah Leen/National Geographic Image Collection
Figure 10.25 Skin Color Is Polygenic.
6/64
AaBBCC
AABbCC
AABBCc
1/64
AABBCC
10.9 Mastering Concepts
How can the environment affect a
phenotype?
10.10 Investigating Life: Heredity and the
Hungry Hordes
• Pink bollworm (Pectinophora gossypiella)
• Pink caterpillars damage cotton crop
• Soil bacterium Bacillus thuringiensis or Bt
– Produces protein toxic to insects
– Not toxic to humans
– Used in organic farming
Figure 10.26 Hungry Caterpillar.
10.10 Investigating Life: Heredity and the
Hungry Hordes
• Produce genetically modified crops that
express Bt toxin
• Farmers must plant non-Bt buffer
– Prevents selective pressure
– Bt resistance genes are recessive
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RR
rr
Susceptible
Non-Btbuffer
Resistant
Bt crop
Resistant parent’s
gametes
Susceptible parent’s
gametes
r
r
R
R
Rr
Rr
Susceptible
Susceptible
Rr
Rr
Susceptible
Susceptible
All offspring are
heterozygous
and susceptible
Figure 10.27 Bt Crops Require Buffers.
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Resistant
Resistant
×
Susceptible
(heterozygous)
×
Susceptible
Susceptible
(heterozygous)
Feed larvae 10 µg/ml purified
Bt toxin for 21 days
Resistant
Feed larvae 1 µg/ml purified
Bt toxin for 11 days
14
Number of larvae
Number of larvae
14
×
7
0
7
0
0
10 20 30 40 50
Larva weight (mg)
0
10 20 30 40 50
Larva weight (mg)
Figure 10.28 Bt Resistance Is Recessive.
10.10 Mastering Concepts
What do you predict will happen to
the incidence of resistance alleles in
pink bollworm populations if farmers
choose not to plant the required
refuge?