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I.
Inheritance
E.
Pleiotropy
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Single gene may affect multiple traits
Single gene products may affect many cells or cell types
in different ways
Ex: Cystic fibrosis, sickle cell disease
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F.
Epistasis
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Presence of certain alleles at one locus can alter
expression of alleles at different locus
Ex: Coat color in dogs
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Color regulated by one allele pair (B = Black, b = brown)
Second allele pair (E = active, e = inactive) regulates
deposition of color in hair
EE and Ee dogs are pigmented, ee dogs are yellow
Gene for pigment deposition is epistatic to gene that codes
for Black or brown pigment
Fig. 14.12
I.
Inheritance
G. Polygenic Inheritance
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Some traits controlled by alleles at multiple loci
Alleles may have additive effects
Ex: Skin color and height in humans
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Skin color governed by alleles at three unlinked loci
(simplified)
Alleles incompletely dominant with additive effects
AABBCC = Darkest skin color
aabbcc = Lightest skin color
Population typically shows normal distribution of trait
Fig. 14.13
II.
Human Genetics
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Requires different methods than those
for animals and plants
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A.
Controlled mating experiments with truebreeding strains not possible
Pedigree Analysis
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Study of readily identifiable traits
Fig. 14.15
III. Human Genetic Disorders
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Most from mutations of single genes
Most autosomal recessive
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A.
Some autosomal dominant
Autosomal Recessive
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Expressed only in homozygous recessive
individuals
Heterozygous individuals = carriers
III.
Human Genetic Disorders
A.
Autosomal Recessive
1.
Phenylketonuria (PKU)
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2.
Inability to synthesize enzyme that converts phenylalanine to
tyrosine
Phenylalanine  toxic compound  nervous system
damage  severe mental retardation
Damage usually occurs just after birth
Preventable; screening + low phenylalanine diet
Most common in people of W. European descent
Cystic fibrosis (CF)
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Abnormal Cl- transport protein  accumulation of
abnormally thick mucus in lungs, pancreas, reproductive
system
Mucus hosts bacteria  infections, tissue damage
Most common genetic disorder in people of W. European
descent
5% of US residents are carriers