Transcript Chapt20 Lecture 13ed Pt 3

Human Biology
Sylvia S. Mader
Michael Windelspecht
Chapter 20
Patterns of
Genetic
Inheritance
Lecture Outline
Part 3
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20.3 Inheritance of Genetic Disorders
Autosomal recessive disorders
of interest
• ________________ – lack of the enzyme that breaks
down fatty acid proteins in lysosomes results in
accumulation
• ________________ – Cl- ions do not pass normally
through a cell membrane, resulting in thick mucus in
lungs and other places, often causing infections
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20.3 Inheritance of Genetic Disorders
Autosomal recessive disorders
of interest
• Phenylketonuria (PKU) – lack of an enzyme needed
to make a certain amino acid; affects nervous
system development
• Sickle-cell disease – red blood cells are sickleshaped rather than __________, resulting in clogged
blood vessels
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20.3 Inheritance of Genetic Disorders
Tay-Sachs disease
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lysosomes
Healthy neuron
bulging lysosomes
Neuron affected by Tay–Sachs
Figure 20.10 Neuron affected by Tay–Sachs disease.
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20.3 Inheritance of Genetic Disorders
Autosomal dominant disorders
of interest
• __________ syndrome – defect in the production of
the elastic connective tissue protein fibrillin; results
in dislocated lens, long limbs and fingers, caved-in
chest, and weak wall of aorta
• Osteogenesis imperfecta – defect in collagen
synthesis; results in weakened, brittle bones
• ______________ – huntington protein has too many
glutamine amino acids, leading to the progressive
degeneration of brain cells
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20.3 Inheritance of Genetic Disorders
Marfan syndrome
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Connective
tissue defects
Skeleton
Chest wall deformities
Long, thin fingers, arms, legs
Scoliosis (curvature of the spine)
Flat feet
Long, narrow face
Loose joints
Heart and blood vessels
Mitral valve
prolapse
Enlargement
of aorta
Eyes
Lungs
Skin
Lens dislocation
Severe nearsightedness
Collapsed lungs
Stretch marks in skin
Recurrent hernias
Dural ectasia: stretching
of the membrane that
holds spinal fluid
Aneurysm
Aortic wall tear
(top right): © Ed Reschke
Figure 20.16 Marfan syndrome.
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20.3 Inheritance of Genetic Disorders
Genetic disorders
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H2O
Cl–
Cl–
Cl
H2O
Cl–
H2O
Cl
nebulizer
many neurons in normal brain
defective
channel
percussion
vest
thick mucus
loss of neurons in Huntington brain
© Pat Pendarvis
(both): Courtesy Dr. Hemachandra Reddy, The Neurological
Science Institute, Oregon Health & Science University
Figure 20.12 Huntington disease.
Figure 20.11 Cystic fibrosis disease.
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20.4 Beyond Simple Inheritance Patterns
Polygenic inheritance
• Polygenic traits – 2 or more sets of alleles
govern 1 trait
– Each dominant allele codes for a product, so
these effects are additive.
– This results in a continuous variation of
phenotypes.
– Environmental effects cause intervening
phenotypes.
– e.g., skin color ranges from very dark to very light
– e.g., height varies among individual humans
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20.4 Beyond Simple Inheritance Patterns
Polygenic inheritance
• Multifactorial trait – a polygenic trait that is
particularly influenced by the environment
– e.g., skin color is influenced by sun exposure
– e.g., height can be affected by nutrition
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20.4 Beyond Simple Inheritance Patterns
Polygenic inheritance
Frequency
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2
3
4
Number of dominant alleles
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5
6
Figure 20.14 Polygenic inheritance and skin color.
Number
most
are
this
height
few
62
short
64
few
66
68
70
72
74
tall
Height in Inches
Figure 20.13 Height is a polygenic trait in humans.
Courtesy University of Connecticut/Peter Morenus, photographer
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20.4 Beyond Simple Inheritance Patterns
Demonstrating environmental
influences on phenotype
• Himalayan rabbit’s coat
color is influenced by
temperature.
• There is an allele
responsible for melanin
production that appears to
be active only at lower
temperatures.
• The extremities have a
lower temperature and
thus the ears, nose, paws,
and tail are dark in color.
Figure 20.15 Himalayan rabbit with temperature-susceptible
coat color.
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