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  • Usually a dominant allele with such severe effects would be expected to occur only as a new mutation and not be transmitted to future generations. But because the onset of Huntington’s disease usually occurs between the ages of 30 and 50, an individual may have children before knowing whether he or she carries the allele. Genetic testing allows some persons who are at risk to determine whether they are carriers. Persons who test positive and do not have children will eventually cause a decrease in the frequency of the allele in the population. Not everyone who is a risk wishes to be tested because anyone who tests positive for the allele must then live with the knowledge that he or she will eventually develop the disease and die.
  • The trait is in each generation and equally distributed among males & females. Every child of an affected individual has a 50% chance of being affected and a 50% chance of being a carrier
  • Caused by a defective gene that disrupts the channel protein regulating the passage of chloride ions out of the body’s cells. Chloride ions are a component of table salt and are prevalent in the body. As a result of this disruption, chloride ions bulid up in the cells. Water then leaves the surrounding fluid and enters the cells by osmosis. This causes the fluid between the cells to become thick and sticky. The abnrmal buildup of mucus in the lungs and pancreas clogs airways and disables digestion. Therapy loosens and removes the mucus. Lung infections are the result of bacterial growth in the mucus. The CF gene is located on chromosome 7 and genetic testing is possible. Gene therapy is in the study phases. Routine CF testing is in the very near future.


  • 1. Chpt. 11.1 Basic Patterns of Human Inheritance
  • 2. Pedigrees
    • Pedigree – a diagram that traces the inheritance of a particular trait through several generations.
    • Carrier – heterozygous individual. They carry the trait but don't express the trait.
  • 3. Reading a Pedigree
  • 4. Inheritance of Human Traits
  • 5. Dominant Genetic Disorders
  • 6. Dominant Genetic Disorders
    • Caused by DOMINANT alleles
    • Such as RR or Rr
  • 7. Huntington’s Disease
    • Rare but lethal genetic disorder (1/10,000)
    • Onset between 30-50 years of age
    • Caused by a rare autosomal (not sex chromosome) dominant allele
    • Lethal disorder – a disease that causes death in most of the individuals who are affected
    • The nervous system undergoes progressive degeneration, resulting in uncontrolled, jerky movements of the head and limbs and mental deterioration
    • No cure or treatment
  • 8. Huntington disease, a disease of the nervous system, is caused by an autosomal dominant gene.
  • 9. Pedigree for Huntington’s Disease
  • 10. Achondroplasia
    • Affects bone growth of individuals (1/25,000)
    • Causes small body size and limbs that are short with large head.
    • Most common form of dwarfism
    • Adult height of 4 feet with normal life expectancy.
    • No cure or treatment
  • 11. Recessive Genetic Disorders
  • 12.  
  • 13. Cystic Fibrosis
    • The most common lethal genetic disorder among white Americans (1/3,500)
    • 1 in 20 white Americans is a carrier
    • 1 in 2000 children born to white Americans inherits the disorder
    • Kills about 500 children/young adults each year
    • Affects the mucus-producing glands, digestive enzymes, and sweat glands
    • Chloride ions are not absorbed into the cells but are excreted in the sweat. Without sufficient chloride ions in the cells, a thick mucus is secreted.
  • 14. Cystic Fibrosis Symptoms
    • Mucus in lungs & digestive tract is thick
    • Breathing is difficult
    • Lung infections are frequent
    • Mucus slows secretion of some digestive enzymes, prevents proper digestion
    • Physical therapy, special diets, & new drugs have raised the average life expectancy
    • No cure
  • 15. Albinism
    • Caused by altered genes, resulting in the absence of the skin pigment melanin in hair and eyes
    • -White hair
    • -Very pale skin
    • -Pink pupils
    • Occurs 1 in 17,000
    • No cure
  • 16. Tay-Sachs Disease
    • Caused by the absence of the enzymes responsible for breaking down fatty acids called gangliosides
    • Gangliosides accumulate in the brain, inflating brain nerve cells and causing mental deterioration.
    • Identified by cherry-red spot in back of the eye.
    • Found on chromosome 15
    • Affects people of Jewish descent (1/2,500)
    • Death by age 5
    • No cure or treatment
  • 17.  
  • 18. Galactosemia
    • Characterized by the inability of the body to digest galactose.
    • Lactose (from milk) breaks down into galactose and glucose. Galactose is broken down by the enzyme GALT. People with galactosemia lack or have a defective GALT.
    • Will result in mental disabilities, enlarged liver and kidney failure.
    • Occurs in 1/50,000-70,000
    • No cure but must restrict lactose/galactose I diet.