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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
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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
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Based on the pedigree, what is the probability that the child in the question will have cystic fibrosis? 
1/6`
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This family has a kid with cystic fibrosis. What is the probability that their next child will have cystic fibrosis?
1/4
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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
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Osteogenesis imperfecta
- Mutation in type 1 collagen
- "Brittle bone disease"
- No cure
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Achondroplasia
- 1/25,000
- Point mutation (G to A) in fibroblast growth factor receptor gene
- Spontaneously inherited mutations exclusively from father
- Homozygous=lethal
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Lebenberg Syndrome
- Caused by deletion/translocation that increases expression of PITX1 gene
- Homeobox gene responsible for body formation (specifically hind limbs)
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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
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What causes Huntington's?
- Caused by expansion of a tri-nucleotide repeat on chromosome 4
- -CAGCAGCAGCAG...
- -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
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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
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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
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What can we do with knowledge from pedigrees?
- Genetic testing and counseling
- This brings the ethical issues of abortion, health insurance, and jobs
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