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Chapter 12
Patterns of Heredity and
Human Genetics
Section 1
Mendelian Inheritance of
Human Traits
• A pedigree is a
representation of
genetic inheritance.
• Symbols are used to
show the trait being
studied and family
• <>
Answer the following about the
above pedigree
• a. What is the sex of I 1?
• b. How many children does IV 2 have?
• c. How many children of IV 12 have
cancer? ____________
• d. List all of the males who have polyps
(carriers) __________
Dominant Autosomal Heredity
• Follow Rule of Dominance
• Tongue curling
• Free earlobes
• Huntington’s disease
Huntington’s Disease
• Lethal genetic disorder
caused by rare autosomal
dominant allele
• Nervous system disintegrates
causing loss of control of
limbs and mental
Huntington’s disease
• Since onset occurs
between ages 30 and 50,
this defect can be
transmitted to new
generations before the
parent knows that he is a
• Genetic testing can
determine if a person is a
• Carriers will get disease
because allele is dominant.
Recessive Autosomal Heredity
• Genetic disorders caused by
recessive alleles.
• Most genetic disorders are
caused by this type of allele.
• Cystic fibrosis, sickle -cell
anemia, Tay - Sachs disease,
Phenylketonuria (PKU).
Cystic Fibrosis
• Most common lethal genetic
disorder in white Americans.
• Characterized by thick mucus
in lungs and digestive tract.
• Food is not digested properly
• Breathing is difficult - frequent
lung infections
Tay- Sachs
• Absence of enzyme that breaks
down a lipid that is produced and
stored in the central nervous
system. Lipid builds up in brain
• Common in Eastern European
Jews and Pennsylvania Dutch.
Symptoms of
Tay-Sachs Disease
• Blindness
• Progressive loss of
• Mental deterioration
• Death by age 5.
• See pg 312 for pedigree
• Most common in people of
Norwegian and Swedish
• Caused by absence of
enzyme that converts
phenylalanine to tyrosine
(amino acids).
Symptoms of PKU
• New born appears normal.
• Once baby starts drinking
milk, which is high in
phenylalanine, damage
• Build up in phenylalanine
causes severe central
nervous system damage
resulting in mental
Treatment of PKU
• All newborns are tested for
• Changes in diet can prevent
New Problems With
• If a homozygous recessive
female becomes pregnant,
high levels of
phenylalanine in her blood
can damage baby.