Mendel and the Gene pt 2

  1. Characteristics of Recessively Inherited Disorders
    • Occurrences can skip a generation
    • Both parents must be at least a carrier (if not affected)
    • Examples:
    • PKU
    • Tay-Sachs
    • Sickle-cell anemia
  2. Cystic Fibrosis
    • Most common lethal genetic in the US
    • Normal allele codes for a membrane protein that transports chloride ions
    • -Missing/defective channels cause a buildup of mucus
    • Average lifespan is 37 years
  3. Based on the pedigree, what is the probability that the child in the question will have cystic fibrosis?Image Upload 2
  4. This family has a kid with cystic fibrosis. What is the probability that their next child will have cystic fibrosis? Image Upload 4
  5. Characteristics of dominantly inherited disorders
    • Cannot skip generations
    • Dominant alleles which cause lethal disease less common than recessive alleles with lethal effects-- it's dominant so you can't be a carrier. They die before they can reproduce
    • Examples:
    • Achondroplasia
    • Ostogenesis imperfecta
    • Liebenberg Syndrome
    • Huntington's Disease
  6. Osteogenesis imperfecta
    • Mutation in type 1 collagen
    • "Brittle bone disease"
    • No cure
  7. Achondroplasia
    • 1/25,000
    • Point mutation (G to A) in fibroblast growth factor receptor gene
    • Spontaneously inherited mutations exclusively from father
    • Homozygous=lethal
  8. Lebenberg Syndrome
    • Caused by deletion/translocation that increases expression of PITX1 gene
    • Homeobox gene responsible for body formation (specifically hind limbs)
  9. Huntington's Disease
    • Symptoms: involuntary movement, behavioral disturbances, dementia
    • Death (usually 15-20 years after onset)
    • -Pneumonia
    • -Heart disease
    • -Suicide
    • Late onset (usually between 35-45)
    • -Allele maintained in population
    • -1/10,000
  10. What causes Huntington's?
    • Caused by expansion of a tri-nucleotide repeat on chromosome 4
    • -Repeats get larger as it is passed down
    • Number of outcomes:
    • up to 28- normal range; won't develop
    • 29-34- individual will not develop HD but next generation is at risk
    • 35-39- some will develop HD; next generation is also at risk
    • 40 or more- individuals will develop HD
  11. X-linked recessive pedigrees
    • Look for an unequal number of males affected
    • There is a pattern of mother to son transmission because the son gets X chromosome from the mom
  12. X-linked dominant pedigrees
    • An affected father will pass it on to ALL of his daughters
    • An affected mother will pass it on to 50% of offspring
  13. What can we do with knowledge from pedigrees?
    • Genetic testing and counseling
    • This brings the ethical issues of abortion, health insurance, and jobs
Card Set
Mendel and the Gene pt 2