Chapter 12 Patterns of Heredity and Human Genetics

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Chapter 12Patterns of Heredity and Human Genetics

• Section 1
• Mendelian Inheritance of Human Traits

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Pedigree

• A pedigree is a graphic representation of genetic
  inheritance.
• Symbols are used to show the trait being studied
  and family relationships

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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) __________

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Dominant Autosomal Heredity

• Follow Rule of Dominance
• Tongue curling
• Free earlobes
• Huntingtons disease

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Huntingtons Disease

• Lethal genetic disorder caused by rare autosomal
  dominant allele
• Nervous system disintegrates causing loss of
  control of limbs and mental deterioration.

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Huntingtons 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 carrier.

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Huntingtons

• Genetic testing can determine if a person is a
  carrier.
• Carriers will get disease because allele is
  dominant.

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www.about-dementia.com/huntingtons/hd-causes.php
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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).

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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

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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 membranes
• Common in Eastern European Jews and Pennsylvania
  Dutch.

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Symptoms of Tay-Sachs Disease

• Blindness
• Progressive loss of movement
• Mental deterioration
• Death by age 5.
• See pg 312 for pedigree

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Phenylketonuria (PKU)

• Most common in people of Norwegian and Swedish
  descent.
• Caused by absence of enzyme that converts
  phenylalanine to tyrosine (amino acids).

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Symptoms of PKU

• New born appears normal.
• Once baby starts drinking milk, which is high in
  phenylalanine, damage occurs

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Symptoms

• Build up in phenylalanine causes severe central
  nervous system damage resulting in mental
  retardation.

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Treatment of PKU

• All newborns are tested for PKU.
• Changes in diet can prevent damage.

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New Problems With PKU

• If a homozygous recessive female becomes
  pregnant, high levels of phenylalanine in her
  blood can damage baby.